{"segment":[{"time":24,"part":[{"title":"\u0110i\u1ec1n bi\u1ec3u th\u1ee9c th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["3x"],["2"]]],"list":[{"point":5,"width":50,"type_input":"","input_hint":"frac","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/12.jpg' \/><\/center>Cho hai s\u1ed1 c\u00f3 t\u1ec9 s\u1ed1 l\u00e0 $\\dfrac {2}{3}$. G\u1ecdi s\u1ed1 b\u00e9 l\u00e0 $x$. S\u1ed1 l\u1edbn l\u00e0:<div class=\"frac123\"><div class=\"ts\">_input_<\/div><div class=\"ms\">_input_<\/div><\/div>","hint":"","explain":"<span class='basic_left'>G\u1ecdi s\u1ed1 b\u00e9 l\u00e0 $x$ ($x>0$)<br\/>V\u00ec hai s\u1ed1 c\u00f3 t\u1ec9 s\u1ed1 l\u00e0 $\\dfrac {2}{3}$ n\u00ean s\u1ed1 l\u1edbn b\u1eb1ng $\\dfrac {3}{2}$ s\u1ed1 b\u00e9. Hay s\u1ed1 l\u1edbn b\u1eb1ng $\\dfrac {3x}{2}$<\/span>"}]}],"id_ques":961},{"time":24,"part":[{"title":"\u0110i\u1ec1n bi\u1ec3u th\u1ee9c th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["x-5"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/10.jpg' \/><\/center>H\u1ea3i v\u00e0 Nam c\u00f9ng xu\u1ea5t ph\u00e1t \u0111i t\u1eeb nh\u00e0 \u0111\u1ebfn tr\u01b0\u1eddng. H\u1ea3i \u0111\u1ebfn tr\u01b0\u1eddng s\u1edbm h\u01a1n Nam $5$ ph\u00fat. N\u1ebfu g\u1ecdi th\u1eddi gian Nam t\u1eeb nh\u00e0 \u0111\u1ebfn tr\u01b0\u1eddng l\u00e0 $x$ (ph\u00fat). Th\u00ec th\u1eddi gian H\u1ea3i \u0111i t\u1eeb nh\u00e0 \u0111\u1ebfn tr\u01b0\u1eddng l\u00e0:_input_(ph\u00fat) ","hint":"","explain":"<span class='basic_left'>V\u00ec H\u1ea3i t\u1eeb nh\u00e0 \u0111\u1ebfn tr\u01b0\u1eddng s\u1edbm h\u01a1n Nam n\u00ean th\u1eddi gian H\u1ea3i \u0111i \u00edt h\u01a1n th\u1eddi gian Nam \u0111i.<br\/>V\u1eady n\u1ebfu g\u1ecdi th\u1eddi gian Nam \u0111i t\u1eeb nh\u00e0 \u0111\u1ebfn tr\u01b0\u1eddng l\u00e0 $x$ (ph\u00fat) th\u00ec th\u1eddi gian H\u1ea3i \u0111\u1ebfn tr\u01b0\u1eddng l\u00e0 $x-5$ (ph\u00fat)<br\/><span class='basic_pink'>V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $x-5$.<\/span><\/span>"}]}],"id_ques":962},{"time":24,"part":[{"title":"Ch\u1ecdn <u>nh\u1eefng<\/u> \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"Ch\u1ecdn \u0111\u01b0\u1ee3c nhi\u1ec1u \u0111\u00e1p \u00e1n","temp":"checkbox","correct":[["2","3"]],"list":[{"point":5,"img":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/12.jpg' \/><\/center>Bi\u1ec3u th\u1ee9c n\u00e0o sau \u0111\u00e2y bi\u1ec3u di\u1ec5n chi\u1ec1u d\u00e0i m\u1ed9t s\u1ee3i d\u00e2y cao su sau khi b\u1ecb k\u00e9o d\u00e0i th\u00eam $20\\%$ \u0111\u1ed9 d\u00e0i.<br\/>G\u1ecdi \u0111\u1ed9 d\u00e0i s\u1ee3i d\u00e2y cao su ban \u0111\u1ea7u l\u00e0 $x$ ($m$).","hint":"Khi b\u1ecb k\u00e9o d\u00e0i th\u00eam $20\\%$ \u0111\u1ed9 d\u00e0i th\u00ec chi\u1ec1u d\u00e0i s\u1ee3i d\u00e2y ban \u0111\u1ea7u t\u0103ng th\u00eam $20\\%$ chi\u1ec1u d\u00e0i.","column":2,"number_true":2,"select":["A. $20x$","B. $120\\%.x$","C. $1,2x$","D. $120x$"],"explain":"<span class='basic_left'>G\u1ecdi chi\u1ec1u d\u00e0i ban \u0111\u1ea7u c\u1ee7a s\u1ee3i d\u00e2y l\u00e0 $x$ ($m$)<br\/>V\u00ec s\u1ee3i d\u00e2y b\u1ecb k\u00e9o d\u00e0i th\u00eam $20\\%$ n\u00ean chi\u1ec1u d\u00e0i t\u0103ng th\u00eam $20\\%x=0,2x$ ($m$)<br\/>V\u1eady chi\u1ec1u d\u00e0i s\u1ee3i d\u00e2y sau khi b\u1ecb k\u00e9o gi\u00e3n l\u00e0 $x+0,2x=1,2x(=120\\%.x)$($m$)<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 B v\u00e0 C.<\/span><\/span>"}]}],"id_ques":963},{"time":24,"part":[{"title":"Ch\u1ecdn <u>nh\u1eefng<\/u> \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"Ch\u1ecdn \u0111\u01b0\u1ee3c nhi\u1ec1u \u0111\u00e1p \u00e1n","temp":"checkbox","correct":[["1","5","6"]],"list":[{"point":5,"img":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/12.jpg' \/><\/center>Bi\u1ec3u th\u1ee9c n\u00e0o sau \u0111\u00e2y bi\u1ec3u di\u1ec5n gi\u00e1 m\u1ed9t chi\u1ebfc \u00e1o gi\u1ea3m $30\\%$<br\/>G\u1ecdi gi\u00e1 ti\u1ec1n c\u1ee7a chi\u1ebfc \u00e1o ban \u0111\u1ea7u l\u00e0 $x$ (\u0111\u1ed3ng)","hint":"","column":2,"number_true":2,"select":["A. $70\\%.x$","B. $130\\%.x$","C. $1,3x$","D. $30x$ ","E. $0,7x$","F. $x-30\\%x$"],"explain":"<span class='basic_left'>G\u1ecdi gi\u00e1 ti\u1ec1n c\u1ee7a chi\u1ebfc \u00e1o ban \u0111\u1ea7u l\u00e0 $x$ (\u0111\u1ed3ng,$x > 0$)<br\/>V\u00ec gi\u00e1 chi\u1ebfc \u00e1o gi\u1ea3m $30\\%$ n\u00ean gi\u00e1 m\u1edbi l\u00e0 $x-30\\%x=70\\%x=0,7x$ (\u0111\u1ed3ng)<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 A, E v\u00e0 F.<\/span><\/span>"}]}],"id_ques":964},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":5,"ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/11.jpg' \/><\/center>Hai xe c\u00f9ng di chuy\u1ec3n t\u1eeb $A$ \u0111\u1ebfn $B$ d\u00e0i $15 km$. Xe th\u1ee9 nh\u1ea5t \u0111i nhanh h\u01a1n xe th\u1ee9 hai $5km\/h$. N\u1ebfu g\u1ecdi th\u1eddi gian xe th\u1ee9 nh\u1ea5t l\u00e0 $x$ (gi\u1edd) th\u00ec v\u1eadn t\u1ed1c xe th\u1ee9 hai l\u00e0:","select":["A. $x-5$","B. $x+5$","C. $\\dfrac {15}{x}-5$","D. $\\dfrac {15}{x}+5$"],"hint":"S\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c li\u00ean h\u1ec7 gi\u1eefa v\u1eadn t\u1ed1c, qu\u00e3ng \u0111\u01b0\u1eddng v\u00e0 th\u1eddi gian.<br\/>Bi\u1ec3u di\u1ec5n v\u1eadn t\u1ed1c c\u1ee7a xe th\u1ee9 nh\u1ea5t theo th\u1eddi gian $x$.","explain":" <span class='basic_left'>G\u1ecdi th\u1eddi gian xe th\u1ee9 nh\u1ea5t l\u00e0 $x$ (gi\u1edd)<br\/>V\u00ec qu\u00e3ng \u0111\u01b0\u1eddng $AB$ d\u00e0i $15 km$ n\u00ean v\u1eadn t\u1ed1c xe th\u1ee9 nh\u1ea5t l\u00e0 $\\dfrac {15}{x}$ ($km\/h$)<br\/>V\u00ec xe th\u1ee9 nh\u1ea5t \u0111i nhanh h\u01a1n xe th\u1ee9 hai $5km\/h$ n\u00ean v\u1eadn t\u1ed1c xe th\u1ee9 hai l\u00e0 $\\dfrac {15}{x}-5$ ($km\/h$)<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 C <\/span><br\/><b>Ghi nh\u1edb:<\/b> \u0110\u1ed1i v\u1edbi b\u00e0i to\u00e1n chuy\u1ec3n \u0111\u1ed9ng, ta n\u00ean l\u1eadp b\u1ea3ng \u0111\u1ec3 t\u00f3m t\u1eaft \u0111\u1ec1 b\u00e0i v\u00e0 \u0111\u1eb7t \u1ea9n th\u00ec quan s\u00e1t d\u1ec5 h\u01a1n:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng($km$)<\/th><th>V\u1eadn t\u1ed1c($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Xe th\u1ee9 nh\u1ea5t<\/td><td>$15$<\/td><td>$\\dfrac {15}{x}$<\/td><td>$x$<\/td><\/tr><tr><td>Xe th\u1ee9 hai<\/td><td>$15$<\/td><td>$\\dfrac {15}{x}-5$<\/td><td><\/td><\/tr><\/table><\/span>","column":2}]}],"id_ques":965},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["150"]]],"list":[{"point":5,"width":50,"type_input":"","input_hint":"frac","ques":"<span class='basic_left'>M\u1ed9t \u00f4 t\u00f4 \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $60 \\,km\/h$ r\u1ed3i quay v\u1ec1 $A$ v\u1edbi v\u1eadn t\u1ed1c $50 \\,km\/h$ bi\u1ebft th\u1eddi gian \u0111i \u00edt h\u01a1n th\u1eddi gian v\u1ec1 l\u00e0 $30$ ph\u00fat. T\u00ednh qu\u00e3ng \u0111\u01b0\u1eddng $AB$.<br\/><b>\u0110\u00e1p s\u1ed1: <\/b>$AB=$ _input_$(km)$<\/span>","hint":"S\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c li\u00ean h\u1ec7 gi\u1eefa v\u1eadn t\u1ed1c, qu\u00e3ng \u0111\u01b0\u1eddng v\u00e0 th\u1eddi gian.","explain":"<span class='basic_left'><br\/><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi \u0111\u1ed9 d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 \u1ea9n v\u00e0 l\u1eadp b\u1ea3ng<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n th\u1eddi gian \u0111i v\u00e0 th\u1eddi gian v\u1ec1 theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh r\u1ed3i k\u1ebft lu\u1eadn<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng($km$)<\/th><th>V\u1eadn t\u1ed1c($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>T\u1eeb $A$ \u0111\u1ebfn $B$<\/td><td>$x$<\/td><td>$60$<\/td><td>$\\dfrac {x}{60}$<\/td><\/tr><tr><td>T\u1eeb $B$ v\u1ec1 $A$<\/td><td>$x$<\/td><td>$50$<\/td><td>$\\dfrac {x}{50}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi \u0111\u1ed9 d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $x$ $(km, x>0)$ <br\/>\u00d4 t\u00f4 \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $60\\,km\/h$ n\u00ean th\u1eddi gian \u0111i l\u00e0 $\\dfrac {x}{60}$ (gi\u1edd)<br\/>\u00d4 t\u00f4 \u0111i t\u1eeb $B$ v\u1ec1 $A$ v\u1edbi v\u1eadn t\u1ed1c $50 \\,km\/h$ n\u00ean th\u1eddi gian v\u1ec1 l\u00e0 $\\dfrac {x}{50}$ (gi\u1edd)<br\/>Th\u1eddi gian \u0111i \u00edt h\u01a1n th\u1eddi gian v\u1ec1 $30$ ph\u00fat $=\\dfrac {1}{2}$ gi\u1edd n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: $\\dfrac {x}{50}-\\dfrac {x}{60}=\\dfrac {1}{2}$<br\/>Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {x}{50}-\\dfrac {x}{60}=\\dfrac {1}{2}\\\\ \\Leftrightarrow \\dfrac {1}{300}x=\\dfrac {1}{2}\\\\ \\Leftrightarrow x=150\\,\\,\\,\\text {(th\u1ecfa m\u00e3n)}$<br\/>V\u1eady qu\u00e3ng \u0111\u01b0\u1eddng $AB$ d\u00e0i $150 \\,km$<br\/><span class='basic_pink'>V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $150$<\/span><br\/><span class='basic_green'>Ghi nh\u1edb:<\/span> <br\/>- C\u00f4ng th\u1ee9c li\u00ean h\u1ec7 gi\u1eefa qu\u00e3ng \u0111\u01b0\u1eddng ($s, km$), v\u1eadn t\u1ed1c ($v, km\/h$) v\u00e0 th\u1eddi gian ($t$, gi\u1edd) l\u00e0: $s=v.t \\Leftrightarrow t=\\dfrac {s}{v}$<br\/><b>L\u01b0u \u00fd: <\/b>Khi gi\u1ea3i b\u00e0i to\u00e1n chuy\u1ec3n \u0111\u1ed9ng, c\u1ea7n th\u1ed1ng nh\u1ea5t \u0111\u01a1n v\u1ecb gi\u1eefa c\u00e1c \u0111\u1ea1i l\u01b0\u1ee3ng. T\u1ee9c l\u00e0 n\u1ebfu \u0111\u01a1n v\u1ecb c\u1ee7a v\u1eadn t\u1ed1c l\u00e0 $km\/h$ th\u00ec qu\u00e3ng \u0111\u01b0\u1eddng l\u00e0 $km$, th\u1eddi gian l\u00e0 gi\u1edd.<\/span>"}]}],"id_ques":966},{"time":24,"part":[{"title":"Ch\u1ecdn <u>nh\u1eefng<\/u> \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"Ch\u1ecdn \u0111\u01b0\u1ee3c nhi\u1ec1u \u0111\u00e1p \u00e1n","temp":"checkbox","correct":[["1","4"]],"list":[{"point":5,"img":"","ques":"Hai ng\u01b0\u1eddi c\u00f9ng xu\u1ea5t ph\u00e1t \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ d\u00e0i $16 \\,km$. Ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t \u0111i nhanh h\u01a1n ng\u01b0\u1eddi th\u1ee9 hai $10 \\,km\/h$. Do \u0111\u00f3, ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t \u0111\u1ebfn s\u1edbm h\u01a1n ng\u01b0\u1eddi th\u1ee9 hai $1$ gi\u1edd $20$ ph\u00fat. T\u00ednh v\u1eadn t\u1ed1c m\u1ed7i ng\u01b0\u1eddi.","hint":"G\u1ecdi $x$ l\u00e0 v\u1eadn t\u1ed1c c\u1ee7a ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t.<br\/>S\u1eed d\u1ee5ng c\u00f4ng th\u1ee9c li\u00ean h\u1ec7 gi\u1eefa qu\u00e3ng \u0111\u01b0\u1eddng, v\u1eadn t\u1ed1c v\u00e0 th\u1eddi gian.","column":2,"number_true":2,"select":["A. $\\dfrac{16}{x-10}-\\dfrac{16}{x}=\\dfrac {4}{3}$","B.$\\dfrac{16}{x}-\\dfrac{16}{x-10}=\\dfrac {4}{3}$","C. $\\dfrac{16}{x-10}-\\dfrac{16}{x}=80$","D. $\\dfrac{16}{x-10}=\\dfrac{16}{x}+\\dfrac {4}{3}$"],"explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi v\u1eadn t\u1ed1c ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n th\u1eddi gian \u0111i v\u00e0 v\u1ec1 theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c ($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t<\/td><td>$16$<\/td><td>$x$<\/td><td>$\\dfrac{16}{x}$<\/td><\/tr><tr><td>Ng\u01b0\u1eddi th\u1ee9 hai<\/td><td>$16$<\/td><td>$x-10$<\/td><td>$\\dfrac{16}{x-10}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi v\u1eadn t\u1ed1c ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0 $x$ ($km\/h$, $x > 0$)<br\/>V\u00ec ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t \u0111i nhanh h\u01a1n ng\u01b0\u1eddi th\u1ee9 hai $10 \\,km\/h$ n\u00ean v\u1eadn t\u1ed1c ng\u01b0\u1eddi th\u1ee9 hai l\u00e0 $x-10$ ($km\/h$)<br\/>Th\u1eddi gian ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $\\dfrac{16}{x}$ (gi\u1edd)<br\/>Th\u1eddi gian ng\u01b0\u1eddi th\u1ee9 hai \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $\\dfrac{16}{x-10}$ (gi\u1edd)<br\/>V\u00ec ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t \u0111\u1ebfn s\u1edbm h\u01a1n ng\u01b0\u1eddi th\u1ee9 hai $1$ gi\u1edd $20$ ph\u00fat $=\\dfrac {4}{3}$ (gi\u1edd) n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac{16}{x-10}-\\dfrac{16}{x}=\\dfrac {4}{3}\\\\ \\Leftrightarrow \\dfrac{16}{x-10}=\\dfrac{16}{x}+\\dfrac {4}{3}$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 A v\u00e0 D<\/span><br\/><b> Ghi nh\u1edb: <\/b> \u0110\u1ed1i v\u1edbi \u0111\u1ea1i l\u01b0\u1ee3ng th\u1eddi gian, \u0111\u1ebfn s\u1edbm h\u01a1n th\u00ec th\u1eddi gian l\u00e0 \u00edt h\u01a1n v\u00e0 ng\u01b0\u1ee3c l\u1ea1i, \u0111\u1ebfn mu\u1ed9n h\u01a1n l\u00e0 th\u1eddi gian nhi\u1ec1u h\u01a1n<\/span>"}]}],"id_ques":967},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["63"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/7.jpg' \/><\/center>M\u1ed9t h\u00ecnh ch\u1eef nh\u1eadt c\u00f3 chu vi l\u00e0 $32cm$ n\u1ebfu t\u0103ng chi\u1ec1u d\u00e0i $1 cm$ v\u00e0 t\u0103ng chi\u1ec1u r\u1ed9ng $2 cm$ th\u00ec di\u1ec7n t\u00edch t\u0103ng $27\\,cm^2$. T\u00ednh di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt.<br\/><b> \u0110\u00e1p s\u1ed1:<\/b> _input_($cm^2$)","hint":"T\u00ednh chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt.","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi chi\u1ec1u d\u00e0i ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b>Bi\u1ec3u di\u1ec5n chi\u1ec1u r\u1ed9ng v\u00e0 c\u00e1c k\u00edch th\u01b0\u1edbc sau khi thay \u0111\u1ed5i theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Chi\u1ec1u d\u00e0i<\/th><th>Chi\u1ec1u r\u1ed9ng<\/th><th>Di\u1ec7n t\u00edch<\/th><\/tr><tr><td>Ban \u0111\u1ea7u<\/td><td>$x$<\/td><td>$16-x$<\/td><td>$x(16-x)$<\/td><\/tr><tr><td>Sau thay \u0111\u1ed5i<\/td><td>$x+1$<\/td><td>$16-x+2$<\/td><td>$(x+1)(18-x)$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi chi\u1ec1u d\u00e0i h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $x$ ($cm$, $x > 0$)<br\/>V\u00ec h\u00ecnh ch\u1eef nh\u1eadt c\u00f3 chu vi l\u00e0 $32\\,cm$ n\u00ean chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $32:2-x=16-x$ ($cm$)<br\/>Di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $x(16-x)$ ($cm^2$)<br\/>Chi\u1ec1u d\u00e0i h\u00ecnh ch\u1eef nh\u1eadt khi t\u0103ng $1\\,cm $ l\u00e0 $x+1$ ($cm$)<br\/>Chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt khi t\u0103ng $2\\, cm$ l\u00e0 $18-x$ ($cm$)<br\/>Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt sau khi thay \u0111\u1ed5i c\u00e1c k\u00edch th\u01b0\u1edbc l\u00e0 $(x+1)(18-x)$ ($cm^2$)<br\/>V\u00ec di\u1ec7n t\u00edch t\u0103ng $27\\,cm^2$ n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $(x+1)(18-x)=x(16-x)+27\\\\ \\Leftrightarrow -x^2+17x+18=-x^2+16x+27\\\\ \\Leftrightarrow x=9\\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady chi\u1ec1u d\u00e0i ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $9\\,cm$, suy ra chi\u1ec1u r\u1ed9ng ban \u0111\u1ea7u l\u00e0 $7\\, cm$<br\/>Do \u0111\u00f3 di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $63\\,cm^2$<br\/><span class='basic_pink'>V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $63$<\/span><\/span>"}]}],"id_ques":968},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["200"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/7.jpg' \/><\/center>Cho m\u1ed9t h\u00ecnh vu\u00f4ng, n\u1ebfu gi\u1ea3m m\u1ed9t c\u1ea1nh \u0111i $10\\%$ v\u00e0 t\u0103ng c\u1ea1nh k\u1ec1 v\u1edbi n\u00f3 th\u00eam $20\\,cm$ th\u00ec ta \u0111\u01b0\u1ee3c m\u1ed9t h\u00ecnh ch\u1eef nh\u1eadt chu vi b\u1eb1ng chu vi h\u00ecnh vu\u00f4ng ban \u0111\u1ea7u. T\u00ednh c\u1ea1nh h\u00ecnh vu\u00f4ng.<br\/><b>\u0110\u00e1p s\u1ed1:<\/b> _input_($cm$)","hint":"","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi c\u1ea1nh h\u00ecnh vu\u00f4ng l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n c\u00e1c k\u00edch th\u01b0\u1edbc sau khi thay \u0111\u1ed5i theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/D8_B21TB1.2.png' \/><\/center><br\/>G\u1ecdi c\u1ea1nh h\u00ecnh vu\u00f4ng l\u00e0 $x$ ($cm$, $x > 0$)<br\/>Chu vi c\u1ee7a h\u00ecnh vu\u00f4ng l\u00e0 $4x$ ($cm$)<br\/>C\u1ea1nh h\u00ecnh vu\u00f4ng sau khi gi\u1ea3m $10\\%$ l\u00e0 $x-10\\%x=0,9x$ ($cm$)<br\/>C\u1ea1nh k\u1ec1 c\u1ea1nh \u0111\u00f3 sau khi t\u0103ng $20\\, cm$ l\u00e0 $x+20$ ($cm$)<br\/>Chu vi h\u00ecnh ch\u1eef nh\u1eadt sau khi thay \u0111\u1ed5i c\u00e1c k\u00edch th\u01b0\u1edbc c\u1ee7a h\u00ecnh vu\u00f4ng l\u00e0 $[0,9x+(x+20)].2$ ($cm$)<br\/>V\u00ec chu vi b\u1eb1ng v\u1edbi chu vi h\u00ecnh vu\u00f4ng n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $[0,9x+(x+20)].2=4x\\\\ \\Leftrightarrow 1,9x+20=2x\\\\ \\Leftrightarrow 0,1x=20\\\\ \\Leftrightarrow x=200 \\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady c\u1ea1nh h\u00ecnh vu\u00f4ng l\u00e0 $200\\,cm$ <br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $200$<\/span><\/span>"}]}],"id_ques":969},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["60"],["50"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/8.jpg' \/><\/center><span class='basic_left'>Hai \u00f4 t\u00f4 c\u00f9ng kh\u1edfi \u0111\u1ed9ng t\u1eeb hai \u0111\u1ecba \u0111i\u1ec3m $A$ v\u00e0 $B$ c\u00e1ch nhau $220 km$. Sau $2$ gi\u1edd hai xe g\u1eb7p nhau. Bi\u1ebft v\u1eadn t\u1ed1c xe \u0111i t\u1eeb $A$ l\u1edbn h\u01a1n v\u1eadn t\u1ed1c xe \u0111i t\u1eeb $B$ l\u00e0 $10km\/h$. T\u00ecm v\u1eadn t\u1ed1c m\u1ed7i xe.<br\/><b>\u0110\u00e1p s\u1ed1:<\/b><br\/>V\u1eadn t\u1ed1c xe \u0111i t\u1eeb $A$ l\u00e0 _input_($km\/h$)<br\/>V\u1eadn t\u1ed1c xe \u0111i t\u1eeb $B$ l\u00e0 _input_($km\/h$)<\/span>","hint":"T\u1ed5ng qu\u00e3ng \u0111\u01b0\u1eddng hai ng\u01b0\u1eddi khi g\u1eb7p nhau l\u00e0 \u0111\u1ed9 d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi v\u1eadn t\u1ed1c ng\u01b0\u1eddi \u0111i t\u1eeb $A$ l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n v\u1eadn t\u1ed1c qu\u00e3ng \u0111\u01b0\u1eddng c\u1ee7a hai ng\u01b0\u1eddi theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c ($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Ng\u01b0\u1eddi \u0111i t\u1eeb $A$<\/td><td>$2x$<\/td><td>$x$<\/td><td>$2$<\/td><\/tr><tr><td>Ng\u01b0\u1eddi \u0111i t\u1eeb $B$<\/td><td>$2(x-10)$<\/td><td>$x-10$<\/td><td>$2$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/D8_B21TB1.1.png' \/><\/center>G\u1ecdi v\u1eadn t\u1ed1c ng\u01b0\u1eddi \u0111i t\u1eeb $A$ l\u00e0 $x$ ($km\/h,\\,x>0$)<br\/>Qu\u00e3ng \u0111\u01b0\u1eddng ng\u01b0\u1eddi \u0111i t\u1eeb $A$ \u0111i \u0111\u01b0\u1ee3c \u0111\u1ebfn l\u00fac g\u1eb7p ng\u01b0\u1eddi \u0111i t\u1eeb $B$ l\u00e0 $2x$ ($km$)<br\/>V\u1eadn t\u1ed1c ng\u01b0\u1eddi \u0111i t\u1eeb $B$ l\u00e0 $x-10$ ($km\/h$)<br\/>Qu\u00e3ng \u0111\u01b0\u1eddng ng\u01b0\u1eddi \u0111i t\u1eeb $B$ \u0111i \u0111\u01b0\u1ee3c \u0111\u1ebfn l\u00fac g\u1eb7p ng\u01b0\u1eddi \u0111i t\u1eeb $A$ l\u00e0 $2(x-10)$ ($km$)<br\/>T\u1ed5ng qu\u00e3ng \u0111\u01b0\u1eddng hai ng\u01b0\u1eddi khi g\u1eb7p nhau l\u00e0 \u0111\u1ed9 d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$2x+2(x-10)=220\\\\ \\Leftrightarrow 4x=240\\\\ \\Leftrightarrow x=60 \\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady v\u1eadn t\u1ed1c ng\u01b0\u1eddi \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $60\\,km\/h$; v\u1eadn t\u1ed1c ng\u01b0\u1eddi \u0111i t\u1eeb $B$ \u0111\u1ebfn $A$ l\u00e0 $50\\,km\/h$<br\/><span class='basic_pink'>V\u1eady c\u00e1c s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $60$ v\u00e0 $50$<\/span><\/span>"}]}],"id_ques":970},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["10"],["13"]]],"list":[{"point":5,"width":50,"type_input":"","input_hint":"frac","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/12.jpg' \/><\/center>M\u1ed9t ph\u00e2n s\u1ed1 c\u00f3 t\u1eed s\u1ed1 b\u00e9 h\u01a1n m\u1eabu s\u1ed1 $3$ \u0111\u01a1n v\u1ecb. N\u1ebfu nh\u00e2n t\u1eed s\u1ed1 v\u1edbi $3$ v\u00e0 th\u00eam m\u1eabu s\u1ed1 $7$ \u0111\u01a1n v\u1ecb th\u00ec \u0111\u01b0\u1ee3c ph\u00e2n s\u1ed1 m\u1edbi b\u1eb1ng ph\u00e2n s\u1ed1 $\\dfrac {3}{2}$. T\u00ecm ph\u00e2n s\u1ed1 ban \u0111\u1ea7u.<br\/><b> \u0110\u00e1p s\u1ed1:<\/b> <div class=\"frac123\"><div class=\"ts\">_input_<\/div><div class=\"ms\">_input_<\/div><\/div>","hint":"G\u1ecdi t\u1eed s\u1ed1 l\u00e0 \u1ea9n r\u1ed3i bi\u1ec3u di\u1ec5n m\u1eabu s\u1ed1 theo \u1ea9n.","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi t\u1eed s\u1ed1 l\u00e0 \u1ea9n, \u0111\u1eb7t \u0111i\u1ec1u ki\u1ec7n cho \u1ea9n.<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n m\u1eabu s\u1ed1 v\u00e0 c\u00e1c \u0111\u1ea1i l\u01b0\u1ee3ng sau khi thay \u0111\u1ed5i.<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi t\u1eed s\u1ed1 l\u00e0 $x$ ($x\\in\\mathbb N^*,\\,0 < x < 10$)<br\/>V\u00ec t\u1eed s\u1ed1 b\u00e9 h\u01a1n m\u1eabu s\u1ed1 $3$ \u0111\u01a1n v\u1ecb n\u00ean m\u1eabu s\u1ed1 l\u00e0 $x+3$<br\/>N\u1ebfu nh\u00e2n t\u1eed s\u1ed1 v\u1edbi $3$ v\u00e0 th\u00eam m\u1eabu s\u1ed1 $7$ \u0111\u01a1n v\u1ecb ta \u0111\u01b0\u1ee3c ph\u00e2n s\u1ed1 m\u1edbi l\u00e0 $\\dfrac {3x}{x+10}$<br\/>Ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$\\dfrac {3x}{x+10}=\\dfrac {3}{2}\\\\ \\Leftrightarrow 6x=3x+30\\\\ \\Leftrightarrow x=10 \\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady ph\u00e2n s\u1ed1 ban \u0111\u1ea7u l\u00e0 $\\dfrac {10}{13}$<\/span>"}]}],"id_ques":971},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["80"]]],"list":[{"point":5,"width":50,"type_input":"","input_hint":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/13.jpg' \/><\/center>M\u1ed9t ca n\u00f4 xu\u00f4i d\u00f2ng t\u1eeb $A$ \u0111\u1ebfn $B$ m\u1ea5t $4$ gi\u1edd v\u00e0 ng\u01b0\u1ee3c d\u00f2ng t\u1eeb $B$ v\u1ec1 $A$ m\u1ea5t $5$ gi\u1edd. T\u00ednh qu\u00e3ng s\u00f4ng $AB$, bi\u1ebft v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc l\u00e0 $2km\/h$.<br\/><b>\u0110\u00e1p s\u1ed1: <\/b> _input_($km$)","hint":"V\u1eadn t\u1ed1c xu\u00f4i d\u00f2ng $=$ v\u1eadn t\u1ed1c ca n\u00f4 $+$ v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc.<br\/>V\u1eadn t\u1ed1c ng\u01b0\u1ee3c d\u00f2ng $=$ v\u1eadn t\u1ed1c ca n\u00f4 $-$ v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc.","explain":"<span class='basic_left'><br\/><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi v\u1eadn t\u1ed1c ca n\u00f4 l\u00e0 \u1ea9n $x$ v\u00e0 bi\u1ec3u di\u1ec5n v\u1eadn t\u1ed1c xu\u00f4i d\u00f2ng v\u00e0 ng\u01b0\u1ee3c d\u00f2ng theo \u1ea9n $x$<br\/><b>B\u01b0\u1edbc 2:<\/b> Vi\u1ebft bi\u1ec3u th\u1ee9c bi\u1ec3u th\u1ecb qu\u00e3ng \u0111\u01b0\u1eddng $AB$ theo v\u1eadn t\u1ed1c xu\u00f4ng d\u00f2ng v\u00e0 v\u1eadn t\u1ed1c ng\u01b0\u1ee3c d\u00f2ng.<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi v\u1eadn t\u1ed1c ca n\u00f4 l\u00e0 $x$ ($km\/h$, $x>0$)<br\/>V\u00ec v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc l\u00e0 $2 km\/h$ n\u00ean v\u1eadn t\u1ed1c ca n\u00f4 khi xu\u00f4i d\u00f2ng l\u00e0 $x+2$ ($km\/h$). <br\/> V\u00ec ca n\u00f4 xu\u00f4i d\u00f2ng t\u1eeb $A$ \u0111\u1ebfn $B$ m\u1ea5t $4$ gi\u1edd n\u00ean qu\u00e3ng s\u00f4ng $AB$ l\u00e0: $4(x+2)$<br\/>V\u1eadn t\u1ed1c khi ca n\u00f4 \u0111i ng\u01b0\u1ee3c d\u00f2ng l\u00e0 $x-2$ ($km\/h$). <br\/> V\u00ec ca n\u00f4 ng\u01b0\u1ee3c d\u00f2ng t\u1eeb $B$ v\u1ec1 $A$ m\u1ea5t $5$ gi\u1edd n\u00ean qu\u00e3ng s\u00f4ng $AB$ l\u00e0 $5(x-2)$<br\/>Ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$4(x+2)=5(x-2)\\\\ \\Leftrightarrow x=18\\,\\,\\,\\text {(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady v\u1eadn t\u1ed1c ca n\u00f4 l\u00e0 $18\\,km\/h$. <br\/> Khi \u0111\u00f3, qu\u00e3ng s\u00f4ng $AB$ l\u00e0 $4(18+2)=80km$<br\/><span class='basic_pink'>S\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $80$<\/span><br\/><b>L\u01b0u \u00fd: <\/b> M\u1ed9t s\u1ed1 b\u00e0i to\u00e1n, n\u1ebfu g\u1ecdi \u1ea9n s\u1ed1 l\u00e0 \u0111\u1ea1i l\u01b0\u1ee3ng c\u1ea7n t\u00ecm th\u00ec vi\u1ec7c l\u1eadp ph\u01b0\u01a1ng tr\u00ecnh s\u1ebd ph\u1ee9c t\u1ea1p h\u01a1n. Do v\u1eady, c\u1ea7n c\u00e2n nh\u1eafc khi g\u1ecdi \u1ea9n \u0111\u1ec3 l\u1eadp v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh d\u1ec5 h\u01a1n.<br\/>Th\u01b0\u1eddng c\u00e1c b\u00e0i to\u00e1n chuy\u1ec3n \u0111\u1ed9ng tr\u00ean d\u00f2ng s\u00f4ng ta n\u00ean g\u1ecdi v\u1eadn t\u1ed1c c\u1ee7a thuy\u1ec1n (ca n\u00f4, b\u00e8,..) l\u00e0 \u1ea9n.<br\/><span class='basic_green'>Ghi nh\u1edb:<\/span> <br\/> V\u1eadn t\u1ed1c xu\u00f4i d\u00f2ng $=$ v\u1eadn t\u1ed1c ca n\u00f4$+$ v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc.<br\/>V\u1eadn t\u1ed1c ng\u01b0\u1ee3c d\u00f2ng $=$ v\u1eadn t\u1ed1c ca n\u00f4 $ -$ v\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc.<\/span>"}]}],"id_ques":972},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["3"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/8.jpg' \/><\/center> M\u1ed9t ng\u01b0\u1eddi \u0111i xe \u0111\u1ea1p t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $20 km\/h$. Sau khi ng\u01b0\u1eddi \u0111\u00f3 \u0111i \u0111\u01b0\u1ee3c $1,5$ gi\u1edd th\u00ec m\u1ed9t ng\u01b0\u1eddi \u0111i xe m\u00e1y t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $40 km\/h$. H\u1ecfi sau bao l\u00e2u k\u1ec3 t\u1eeb l\u00fac xe \u0111\u1ea1p b\u1eaft \u0111\u1ea7u \u0111i hai xe g\u1eb7p nhau?<br\/><b>\u0110\u00e1p s\u1ed1:<\/b>_input_(gi\u1edd)","hint":"Hai ng\u01b0\u1eddi g\u1eb7p nhau t\u1ee9c l\u00e0 qu\u00e3ng \u0111\u01b0\u1eddng h\u1ecd \u0111i \u0111\u01b0\u1ee3c b\u1eb1ng nhau. Th\u1eddi gian ng\u01b0\u1eddi \u0111i xe m\u00e1y \u0111i \u0111\u01b0\u1ee3c \u00edt h\u01a1n th\u1eddi gian ng\u01b0\u1eddi \u0111i xe \u0111\u1ea1p.","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi th\u1eddi gian h\u1ecd g\u1eb7p nhau l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n qu\u00e3ng \u0111\u01b0\u1eddng c\u1ee7a hai ng\u01b0\u1eddi theo \u1ea9n<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh t\u1eeb gi\u1ea3 thi\u1ebft<br\/><b>B\u01b0\u1edbc 4:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Xe \u0111\u1ea1p<\/td><td>$20x$<\/td><td>$20$<\/td><td>$x$<\/td><\/tr><tr><td>Xe m\u00e1y<\/td><td>$40(x-1,5)$<\/td><td>$40$<\/td><td>$x-1,5$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi th\u1eddi gian hai ng\u01b0\u1eddi g\u1eb7p nhau l\u00e0 $x$ (gi\u1edd, $x>1,5$)<br\/>V\u00ec sau khi ng\u01b0\u1eddi \u0111i xe \u0111\u1ea1p \u0111i \u0111\u01b0\u1ee3c $1,5$ gi\u1edd ng\u01b0\u1eddi \u0111i xe m\u00e1y m\u1edbi \u0111i n\u00ean th\u1eddi gian ng\u01b0\u1eddi \u0111i xe m\u00e1y \u0111i \u0111\u1ebfn khi g\u1eb7p nhau l\u00e0 $x-1,5$ (gi\u1edd)<br\/>Qu\u00e3ng \u0111\u01b0\u1eddng ng\u01b0\u1eddi \u0111i xe \u0111\u1ea1p \u0111i l\u00e0 $20x$ ($km$)<br\/>Qu\u00e3ng \u0111\u01b0\u1eddng ng\u01b0\u1eddi \u0111i xe m\u00e1y \u0111i l\u00e0 $40(x-1,5)$ ($km$)<br\/>Hai ng\u01b0\u1eddi g\u1eb7p nhau n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $20x=40(x-1,5)\\\\ \\Leftrightarrow 20x=40x-60\\\\ \\Leftrightarrow x=3\\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady sau $3$ gi\u1edd hai xe g\u1eb7p nhau.<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $3$<\/span><\/span>"}]}],"id_ques":973},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/14h.jpg' \/><\/center> <span class='basic_left'>M\u1ed9t xe t\u1ea3i d\u1ef1 \u0111\u1ecbnh \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $54 km\/h$. Nh\u01b0ng khi \u0111i \u0111\u01b0\u1ee3c $24$ ph\u00fat th\u00ec g\u1eb7p \u0111\u01b0\u1eddng kh\u00f3 \u0111i n\u00ean v\u1eadn t\u1ed1c tr\u00ean qu\u00e3ng \u0111\u01b0\u1eddng c\u00f2n l\u1ea1i l\u00e0 $40 km\/h$. Do v\u1eady xe \u0111\u00e3 \u0111\u1ebfn mu\u1ed9n so v\u1edbi d\u1ef1 \u0111\u1ecbnh $18$ ph\u00fat. H\u1ecfi qu\u00e3ng \u0111\u01b0\u1eddng $AB$ d\u00e0i bao nhi\u00eau $km$?<br\/>G\u1ecdi qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $x$ ($km,\\,x>0$). C\u00f3 b\u1ea3ng t\u00f3m t\u1eaft c\u00e1c \u0111\u1ea1i l\u01b0\u1ee3ng b\u00e0i to\u00e1n.<\/span><br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>D\u1ef1 \u0111\u1ecbnh <\/td><td>$x$<\/td><td>$54$<\/td><td>$\\dfrac{x}{54}$<\/td><\/tr><tr><td>\u0110o\u1ea1n \u0111\u01b0\u1eddng \u0111\u1ea7u<\/td><td>$?2$<\/td><td>$?1$<\/td><td>$\\dfrac {2}{5}$<\/td><\/tr><tr><td>\u0110o\u1ea1n \u0111\u01b0\u1eddng x\u1ea5u<\/td><td>$x-?2$<\/td><td>$40$<\/td><td>$?3$<\/td><\/tr><\/table><br\/>C\u00e1c bi\u1ec3u th\u1ee9c c\u1ea7n \u0111i\u1ec1n v\u00e0o b\u1ea3ng theo th\u1ee9 t\u1ef1 $?1$, $?2$ v\u00e0 $?3$ l\u00e0:","select":["A. $54;\\,\\dfrac {108}{5};\\,\\dfrac {x}{40}-\\dfrac {27}{50}$","B. $40;\\,16;\\,\\dfrac{x}{54}-24$","C. $54;\\,\\dfrac {108}{5};\\,\\dfrac{x}{54}-24-18$","D. $40;\\,16;\\,\\dfrac{x}{54}-24-18$"],"hint":"","explain":" <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/>\u0110\u00e2y l\u00e0 b\u00e0i to\u00e1n chuy\u1ec3n \u0111\u1ed9ng kh\u00f3, d\u1ea1ng d\u1ef1 \u0111\u1ecbnh v\u00e0 th\u1ef1c t\u1ebf. <br\/><b>B\u01b0\u1edbc 1:<\/b><br\/> Nh\u1eadn x\u00e9t th\u1ea5y: C\u00f3 hai giai \u0111o\u1ea1n chuy\u1ec3n \u0111\u1ed9ng l\u1edbn l\u00e0 th\u1ef1c t\u1ebf v\u00e0 d\u1ef1 ki\u1ebfn, trong th\u1ef1c t\u1ebf l\u1ea1i c\u00f3 hai giai \u0111o\u1ea1n chuy\u1ec3n \u0111\u1ed9ng n\u1eefa.<br\/><b>B\u01b0\u1edbc 2:<\/b> L\u1eadp b\u1ea3ng nh\u01b0 tr\u00ean.<br\/><b>B\u01b0\u1edbc 3:<\/b> G\u1ecdi \u1ea9n v\u00e0 ho\u00e0n thi\u1ec7n b\u1ea3ng.<br\/><b>B\u01b0\u1edbc 4:<\/b> D\u1ef1a v\u00e0o d\u1eef ki\u1ec7n ch\u01b0a s\u1eeda d\u1ee5ng khi l\u1eadp b\u1ea3ng \u0111\u1ec3 l\u1eadp ph\u01b0\u01a1ng tr\u00ecnh.<br\/><b>B\u01b0\u1edbc 5:<\/b> Gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 k\u1ebft lu\u1eadn<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>D\u1ef1 \u0111\u1ecbnh <\/td><td>$x$<\/td><td>$54$<\/td><td>$\\dfrac{x}{54}$<\/td><\/tr><tr><td>\u0110o\u1ea1n \u0111\u01b0\u1eddng \u0111\u1ea7u<\/td><td>$\\dfrac {108}{5}$<\/td><td>$54$<\/td><td>$\\dfrac {2}{5}$<\/td><\/tr><tr><td>\u0110o\u1ea1n \u0111\u01b0\u1eddng x\u1ea5u<\/td><td>$x-\\dfrac {108}{5}$<\/td><td>$40$<\/td><td>$\\dfrac {x}{40}-\\dfrac {27}{50}$<\/td><\/tr><\/table><br\/>G\u1ecdi qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $x$ ($km,\\,x>0$)<br\/>Th\u1eddi gian d\u1ef1 \u0111\u1ecbnh \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0: $\\dfrac{x}{54}$ (gi\u1edd)<br\/>Trong \u0111o\u1ea1n \u0111\u01b0\u1eddng \u0111\u1ea7u, v\u1edbi v\u1eadn t\u1ed1c theo d\u1ef1 \u0111\u1ecbnh l\u00e0 $54\\,km\/h$ \u0111i trong $24$ ph\u00fat $=\\dfrac {2}{5}$ gi\u1edd, xe \u0111i \u0111\u01b0\u1ee3c $54.\\dfrac {2}{5}=\\dfrac {108}{5}$ ($km$)<br\/>Khi \u0111\u00f3, \u0111o\u1ea1n \u0111\u01b0\u1eddng c\u00f2n l\u1ea1i l\u00e0 $x-\\dfrac {108}{5}$ ($km$)<br\/>V\u00ec g\u1eb7p \u0111\u01b0\u1eddng kh\u00f3 \u0111i n\u00ean v\u1eadn t\u1ed1c tr\u00ean qu\u00e3ng \u0111\u01b0\u1eddng c\u00f2n l\u1ea1i l\u00e0 $40 km\/h$, ta c\u00f3 th\u1eddi gian \u0111i tr\u00ean qu\u00e3ng \u0111\u01b0\u1eddng x\u1ea5u l\u00e0 $\\left(x-\\dfrac {108}{5}\\right):40=\\dfrac {x}{40}-\\dfrac {27}{50}$<br\/>Do v\u1eady, t\u1ed5ng th\u1eddi gian th\u1ef1c t\u1ebf xe \u0111i l\u00e0 $\\dfrac {2}{5}+\\dfrac {x}{40}-\\dfrac {27}{50}$<br\/>V\u00ec xe \u0111\u00e3 \u0111\u1ebfn mu\u1ed9n so v\u1edbi d\u1ef1 \u0111\u1ecbnh $18$ ph\u00fat $=\\dfrac {3}{10}$ gi\u1edd n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$\\dfrac{x}{54}+\\dfrac {3}{10}=\\dfrac {2}{5}+\\dfrac {x}{40}-\\dfrac {27}{50}$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 A<\/span><br\/><span class='basic_green'>Ghi nh\u1edb: <\/span>\u0110\u1ed1i v\u1edbi d\u1ea1ng to\u00e1n chuy\u1ec3n \u0111\u1ed9ng ph\u1ee9c t\u1ea1p nhi\u1ec1u giai \u0111o\u1ea1n chuy\u1ec3n \u0111\u1ed9ng, ta n\u00ean l\u1eadp b\u1ea3ng \u0111\u1ec3 h\u1ec7 th\u1ed1ng l\u1ea1i c\u00e1c \u0111\u1ea1i l\u01b0\u1ee3ng v\u00e0 \u1ea9n t\u1ed1t h\u01a1n \u0111\u1ed3ng th\u1eddi tr\u00e1nh nh\u1ea7m l\u1eabn v\u00e0 thi\u1ebfu s\u00f3t.<\/span>","column":2}]}],"id_ques":974},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["22"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/16.jpg' \/><\/center> C\u00e1ch \u0111\u00e2y $10$ n\u0103m tu\u1ed5i b\u1ed1 g\u1ea5p $3$ l\u1ea7n tu\u1ed5i con v\u00e0 sau hai n\u0103m n\u1eefa, tu\u1ed5i b\u1ed1 g\u1ea5p $2$ l\u1ea7n tu\u1ed5i con. T\u00ednh tu\u1ed5i c\u1ee7a con hi\u1ec7n nay.<br\/><b>\u0110\u00e1p s\u1ed1:<\/b> Tu\u1ed5i con l\u00e0 _input_ (tu\u1ed5i)","hint":"G\u1ecdi tu\u1ed5i con hi\u1ec7n nay l\u00e0 \u1ea9n","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>$10$ n\u0103m tr\u01b0\u1edbc<\/th><th>Hi\u1ec7n nay<\/th><th>$2$ n\u0103m sau<\/th><\/tr><tr><td>Tu\u1ed5i con<\/td><td>$x-10$<\/td><td>$x$<\/td><td>$x+2$<\/td><\/tr><tr><td>Tu\u1ed5i b\u1ed1<\/td><td>$3(x-10)$<\/td><td><\/td><td>$2(x+2)$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi tu\u1ed5i con hi\u1ec7n nay l\u00e0 $x$ (tu\u1ed5i, $x > 10,\\, x\\in \\mathbb N$)<br\/>C\u00e1ch \u0111\u00e2y $10$ n\u0103m, con $x-10$ (tu\u1ed5i)<br\/>V\u00ec c\u00e1ch \u0111\u00e2y $10$ n\u0103m tu\u1ed5i b\u1ed1 g\u1ea5p $3$ l\u1ea7n tu\u1ed5i con n\u00ean tu\u1ed5i b\u1ed1 l\u00e0 $3(x-10)$ (tu\u1ed5i)<br\/>Tu\u1ed5i con sau hai n\u0103m n\u1eefa l\u00e0 $x+2$ (tu\u1ed5i)<br\/>V\u00ec sau hai n\u0103m n\u1eefa, tu\u1ed5i b\u1ed1 g\u1ea5p $2$ l\u1ea7n tu\u1ed5i con n\u00ean tu\u1ed5i b\u1ed1 sau hai n\u0103m n\u1eefa l\u00e0 $2(x+2)$<br\/>Tu\u1ed5i b\u1ed1 hai n\u0103m n\u1eefa h\u01a1n tu\u1ed5i b\u1ed1 $10$ n\u0103m tr\u01b0\u1edbc l\u00e0 $12$ tu\u1ed5i n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$2(x+2)=3(x-10)+12\\\\ \\Leftrightarrow 2x+4=3x-18\\\\ \\Leftrightarrow x=22$<br\/>V\u1eady hi\u1ec7n nay con $22$ tu\u1ed5i.<br\/><span class='basic_pink'>V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $22$<\/span><\/span>"}]}],"id_ques":975},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["72"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv2/img\/11.jpg' \/><\/center>B\u00ecnh k\u00e9m \u00f4ng $58$ tu\u1ed5i. Hi\u1ec7n nay, tu\u1ed5i c\u1ee7a \u00f4ng B\u00ecnh b\u1eb1ng t\u1ed5ng s\u1ed1 tu\u1ed5i c\u1ee7a cha B\u00ecnh v\u00e0 hai l\u1ea7n tu\u1ed5i c\u1ee7a B\u00ecnh v\u00e0 n\u1ebfu c\u1ed9ng t\u1ed5ng s\u1ed1 tu\u1ed5i c\u1ee7a c\u1ea3 ba ng\u01b0\u1eddi th\u00ec \u0111\u01b0\u1ee3c $130$ tu\u1ed5i. T\u00ednh tu\u1ed5i c\u1ee7a \u00f4ng B\u00ecnh hi\u1ec7n nay.<br\/><b>\u0110\u00e1p s\u1ed1: <\/b> _input_(tu\u1ed5i)","hint":"G\u1ecdi tu\u1ed5i \u00f4ng B\u00ecnh hi\u1ec7n nay l\u00e0 $x$, bi\u1ec3u di\u1ec5n tu\u1ed5i c\u1ee7a B\u00ecnh v\u00e0 tu\u1ed5i cha B\u00ecnh theo \u1ea9n $x$ ","explain":"<span class='basic_left'>G\u1ecdi s\u1ed1 tu\u1ed5i hi\u1ec7n nay c\u1ee7a \u00f4ng B\u00ecnh l\u00e0 $x$ (tu\u1ed5i, $x\\in \\mathbb N^*,\\,x > 58$)<br\/>V\u00ec B\u00ecnh k\u00e9m \u00f4ng $58$ tu\u1ed5i n\u00ean tu\u1ed5i B\u00ecnh hi\u1ec7n nay l\u00e0 $x-58$ (tu\u1ed5i)<br\/>V\u00ec t\u1ed5ng s\u1ed1 tu\u1ed5i c\u1ee7a ba ng\u01b0\u1eddi l\u00e0 130 tu\u1ed5i n\u00ean tu\u1ed5i c\u1ee7a cha B\u00ecnh l\u00e0 $130-x-(x-58)=188-2x$ (tu\u1ed5i)<br\/>V\u00ec tu\u1ed5i c\u1ee7a \u00f4ng B\u00ecnh b\u1eb1ng t\u1ed5ng s\u1ed1 tu\u1ed5i c\u1ee7a cha B\u00ecnh v\u00e0 hai l\u1ea7n tu\u1ed5i c\u1ee7a B\u00ecnh n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$x=188-2x+2(x-58)\\\\ \\Leftrightarrow x=188-2x+2x-116\\\\ \\Leftrightarrow x=72\\,\\,\\text {(th\u1ecfa m\u00e3n)}$<br\/>V\u1eady hi\u1ec7n nay \u00f4ng B\u00ecnh $72$ tu\u1ed5i.<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $72$<\/span><\/span>"}]}],"id_ques":976},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":5,"ques":"M\u1ed9t \u0111\u1ed9i s\u1ea3n xu\u1ea5t d\u1ef1 \u0111\u1ecbnh ph\u1ea3i l\u00e0m m\u1ed9t s\u1ed1 d\u1ee5ng c\u1ee5 trong $30$ ng\u00e0y. Do m\u1ed7i ng\u00e0y \u0111\u00e3 v\u01b0\u1ee3t n\u0103ng su\u1ea5t so v\u1edbi d\u1ef1 \u0111\u1ecbnh $10$ d\u1ee5ng c\u1ee5 n\u00ean kh\u00f4ng nh\u1eefng \u0111\u00e3 l\u00e0m th\u00eam \u0111\u01b0\u1ee3c $20$ d\u1ee5ng c\u1ee5 m\u00e0 t\u1ed5 \u0111\u00f3 c\u00f2n l\u00e0m xong tr\u01b0\u1edbc th\u1eddi h\u1ea1n $7$ ng\u00e0y.T\u00ednh s\u1ed1 d\u1ee5ng c\u1ee5 m\u00e0 t\u1ed5 s\u1ea3n xu\u1ea5t \u0111\u00f3 ph\u1ea3i l\u00e0m theo k\u1ebf ho\u1ea1ch.<br\/>G\u1ecdi $x$ l\u00e0 s\u1ed1 d\u1ee5ng c\u1ee5 m\u00e0 t\u1ed5 s\u1ea3n xu\u1ea5t theo k\u1ebf ho\u1ea1ch. Ph\u01b0\u01a1ng tr\u00ecnh bi\u1ec3u th\u1ecb b\u00e0i to\u00e1n l\u00e0:","hint":"\u0110\u00e2y l\u00e0 d\u1ea1ng to\u00e1n n\u0103ng su\u1ea5t: Kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c $=$ th\u1eddi gian ho\u00e0n th\u00e0nh $\\times $ n\u0103ng su\u1ea5t lao \u0111\u1ed9ng","select":["A. $\\dfrac {x}{30}.23=x+20$","B. $\\left(\\dfrac {x}{30}+10\\right).23+20=x$","C. $\\left(\\dfrac {x}{30}+10\\right).23=x+20$","D. $\\left(\\dfrac {x}{30}+10\\right).23=x$"],"explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><table><tr><th><\/th><th>S\u1ed1 s\u1ea3n ph\u1ea9m<\/th><th>N\u0103ng su\u1ea5t<\/th><th>S\u1ed1 ng\u00e0y<\/th><\/tr><tr><td>D\u1ef1 ki\u1ebfn<\/td><td>$x$<\/td><td>$\\dfrac {x}{30}$<\/td><td>$30$<\/td><\/tr><tr><td>Th\u1ef1c t\u1ebf<\/td><td>$23.\\left(\\dfrac {x}{30}+10\\right)$<\/td><td>$\\dfrac {x}{30}+10$<\/td><td>$23$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi s\u1ed1 d\u1ee5ng c\u1ee5 m\u00e0 t\u1ed5 s\u1ea3n xu\u1ea5t theo k\u1ebf ho\u1ea1ch l\u00e0 $x$ (d\u1ee5ng c\u1ee5, $x\\in\\mathbb N^*$)<br\/>N\u0103ng su\u1ea5t d\u1ef1 ki\u1ebfn l\u00e0 $\\dfrac {x}{30}$ (d\u1ee5ng c\u1ee5 \/ ng\u00e0y)<br\/>Th\u1ef1c t\u1ebf m\u1ed9t ng\u00e0y, t\u1ed5 s\u1ea3n xu\u1ea5t l\u00e0m \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {x}{30}+10$ (d\u1ee5ng c\u1ee5)<br\/>V\u00ec t\u1ed5 \u0111\u00f3 l\u00e0m xong tr\u01b0\u1edbc th\u1eddi h\u1ea1n $7$ ng\u00e0y n\u00ean s\u1ed1 ng\u00e0y l\u00e0m th\u1ef1c t\u1ebf l\u00e0 $23$ ng\u00e0y.<br\/>T\u1ed5ng s\u1ed1 d\u1ee5ng c\u1ee5 l\u00e0m th\u1ef1c t\u1ebf l\u00e0 $\\left(\\dfrac {x}{30}+10\\right).23$ (d\u1ee5ng c\u1ee5)<br\/>V\u00ec th\u1ef1c t\u1ebf t\u1ed5 s\u1ea3n xu\u1ea5t l\u00e0m th\u00eam \u0111\u01b0\u1ee3c $20$ d\u1ee5ng c\u1ee5 n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$\\left(\\dfrac {x}{30}+10\\right).23=x+20$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 $C$<\/span><\/span>","column":2}]}],"id_ques":977},{"time":24,"part":[{"time":3,"title":"Hai v\u00f2i n\u01b0\u1edbc c\u00f9ng ch\u1ea3y v\u00e0o m\u1ed9t c\u00e1i b\u1ec3 th\u00ec $72$ ph\u00fat th\u00ec \u0111\u1ea7y b\u1ec3. N\u1ebfu v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y $1$ gi\u1edd r\u1ed3i v\u00f2i th\u1ee9 hai ch\u1ea3y m\u1ed9t m\u00ecnh trong $1$ gi\u1edd $30$ ph\u00fat n\u1eefa th\u00ec \u0111\u1ea7y b\u1ec3. H\u1ecfi n\u1ebfu m\u1ed7i v\u00f2i ch\u1ea3y m\u1ed9t m\u00ecnh th\u00ec sau bao l\u00e2u s\u1ebd \u0111\u1ea7y b\u1ec3.","title_trans":"S\u1eafp x\u1ebfp c\u00e1c b\u01b0\u1edbc \u0111\u1ec3 l\u1eadp ph\u01b0\u01a1ng tr\u00ecnh c\u1ee7a b\u00e0i to\u00e1n tr\u00ean","temp":"sequence","correct":[[[4],[1],[5],[2],[3]]],"list":[{"point":5,"image":"img\/1.png","left":["Trong $1$ gi\u1edd $30$ ph\u00fat $=\\dfrac {3}{2}$ gi\u1edd v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {3}{2}.\\left(\\dfrac {5}{6}-\\dfrac {1}{x}\\right)$ (b\u1ec3)","G\u1ecdi th\u1eddi gian v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y m\u1ed9t m\u00ecnh \u0111\u1ea7y b\u1ec3 l\u00e0 $x$ (gi\u1edd, $x > 0$)<br\/>M\u1ed9t gi\u1edd v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {1}{x}$ (b\u1ec3)","V\u00ec v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y $1$ gi\u1edd r\u1ed3i v\u00f2i th\u1ee9 hai ch\u1ea3y m\u1ed9t m\u00ecnh trong $1$ gi\u1edd $30$ ph\u00fat n\u1eefa th\u00ec \u0111\u1ea7y b\u1ec3 n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: $\\dfrac {1}{x}+\\dfrac {3}{2}.\\left(\\dfrac {5}{6}-\\dfrac {1}{x}\\right)=1$","V\u00ec c\u1ea3 hai v\u00f2i ch\u1ea3y v\u00e0o b\u1ec3 m\u1ea5t $72$ ph\u00fat $=\\dfrac {6}{5}$ gi\u1edd th\u00ec \u0111\u1ea7y b\u1ec3.<br\/>N\u00ean m\u1ed7i gi\u1edd hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $1:\\dfrac {6}{5}=\\dfrac {5}{6}$ (b\u1ec3)","Do v\u1eady, m\u1ed9t gi\u1edd v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {5}{6}-\\dfrac {1}{x}$ (b\u1ec3)"],"top":100,"hint":"\u0110\u00e2y l\u00e0 b\u00e0i to\u00e1n n\u0103ng su\u1ea5t (l\u00e0m chung - l\u00e0m ri\u00eang) m\u00e0 kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c kh\u00f4ng c\u1ee5 th\u1ec3 l\u00e0 bao nhi\u00eau n\u00ean ta coi vi\u1ec7c ho\u00e0n th\u00e0nh c\u00f4ng vi\u1ec7c l\u00e0 $1$ \u0111\u01a1n v\u1ecb.","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi th\u1eddi gian ho\u00e0n th\u00e0nh c\u1ee7a v\u00f2i $1$ l\u00e0 $x$<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n $1$ gi\u1edd v\u00f2i m\u1ed9t ch\u1ea3y \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 3:<\/b> Bi\u1ec3u di\u1ec5n $1$ gi\u1edd v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 4:<\/b> Bi\u1ec3u di\u1ec5n $1$ gi\u1edd $30$ ph\u00fat v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c<br\/><b>B\u01b0\u1edbc 5:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi th\u1eddi gian v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y m\u1ed9t m\u00ecnh \u0111\u1ea7y b\u1ec3 l\u00e0 $x$ (gi\u1edd, $x > 0$)<br\/>M\u1ed9t gi\u1edd v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {1}{x}$ (b\u1ec3)<br\/>V\u00ec c\u1ea3 hai v\u00f2i ch\u1ea3y v\u00e0o b\u1ec3 m\u1ea5t $72$ ph\u00fat $=\\dfrac {6}{5}$ gi\u1edd th\u00ec \u0111\u1ea7y b\u1ec3.<br\/>N\u00ean m\u1ed7i gi\u1edd hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $1:\\dfrac {6}{5}=\\dfrac {5}{6}$ (b\u1ec3)<br\/>Do v\u1eady, m\u1ed9t gi\u1edd v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {5}{6}-\\dfrac {1}{x}$ (b\u1ec3)<br\/>Trong $1$ gi\u1edd $30$ ph\u00fat $=\\dfrac {3}{2}$ gi\u1edd v\u00f2i hai ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {3}{2}.\\left(\\dfrac {5}{6}-\\dfrac {1}{x}\\right)$ (b\u1ec3)<br\/>V\u00ec v\u00f2i th\u1ee9 nh\u1ea5t ch\u1ea3y $1$ gi\u1edd r\u1ed3i v\u00f2i th\u1ee9 hai ch\u1ea3y m\u1ed9t m\u00ecnh trong $1$ gi\u1edd $30$ ph\u00fat n\u1eefa th\u00ec \u0111\u1ea7y b\u1ec3 n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {1}{x}+\\dfrac {3}{2}.\\left(\\dfrac {5}{6}-\\dfrac {1}{x}\\right)=1$<br\/><span class='basic_green'>Ghi nh\u1edb: <\/span><br\/>- \u0110\u00e2y l\u00e0 d\u1ea1ng to\u00e1n c\u00f4ng vi\u1ec7c l\u00e0m chung \u2013 l\u00e0m ri\u00eang (d\u1ea1ng to\u00e1n \u0111\u1eb7c bi\u1ec7t c\u1ee7a to\u00e1n n\u0103ng su\u1ea5t lao \u0111\u1ed9ng). Kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c kh\u00f4ng \u0111\u01b0\u1ee3c cho m\u1ed9t s\u1ed1 l\u01b0\u1ee3ng c\u1ee5 th\u1ec3 l\u00e0 bao nhi\u00eau. Ta th\u01b0\u1eddng quy \u01b0\u1edbc c\u00f4ng vi\u1ec7c ho\u00e0n th\u00e0nh l\u00e0 $1$.<br\/> V\u1edbi b\u00e0i to\u00e1n tr\u00ean, c\u00f4ng vi\u1ec7c l\u00e0 $1$ b\u1ec3 n\u01b0\u1edbc.<br\/>N\u1ebfu m\u1ed9t v\u00f2i ch\u1ea3y m\u1ed9t m\u00ecnh $a$ gi\u1edd \u0111\u1ea7y b\u1ec3 th\u00ec 1 gi\u1edd v\u00f2i s\u1ebd ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{a}$ b\u1ec3. <br\/>N\u1ebfu m\u1ed9t v\u00f2i hai ch\u1ea3y m\u1ed9t m\u00ecnh $b$ gi\u1edd \u0111\u1ea7y b\u1ec3 th\u00ec $1$ gi\u1edd v\u00f2i \u0111\u00f3 ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1} {b}$ b\u1ec3.<br\/>V\u00e0 n\u1ebfu hai v\u00f2i c\u00f9ng ch\u1ea3y trong $c$ gi\u1edd th\u00ec \u0111\u1ea7y b\u1ec3 th\u00ec $1$ gi\u1edd c\u1ea3 hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{c}$ b\u1ec3<br\/>Ta lu\u00f4n c\u00f3: $a>c;b>c$ v\u00e0 $\\left\\{\\begin{align}& \\dfrac {1}{a}=\\dfrac{1}{c}-\\dfrac {1}{b}\\\\ &\\dfrac {1}{b}=\\dfrac{1}{c}-\\dfrac {1}{a}\\\\ \\end{align}\\right.$<\/span>"}]}],"id_ques":978},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["60"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"Hai \u0111\u1ed9i c\u00f4ng nh\u00e2n d\u1ef1 ki\u1ebfn l\u00e0m m\u1ed9t con \u0111\u01b0\u1eddng trong $20$ ng\u00e0y th\u00ec xong. Hai \u0111\u1ed9i \u0111\u00e3 l\u00e0m chung trong $4$ ng\u00e0y r\u1ed3i \u0111\u1ed9i m\u1ed9t chuy\u1ec3n sang l\u00e0m vi\u1ec7c kh\u00e1c. \u0110\u1ed9i hai ti\u1ebfp t\u1ee5c l\u00e0m $10$ n\u00e0y n\u1eefa th\u00ec chuy\u1ec3n sang c\u00f4ng vi\u1ec7c kh\u00e1c. \u0110\u1ed9i m\u1ed9t tr\u1edf v\u1ec1 l\u00e0m ti\u1ebfp trong $28$ ng\u00e0y th\u00ec xong. H\u1ecfi n\u1ebfu l\u00e0m m\u1ed9t m\u00ecnh th\u00ec \u0111\u1ed9i m\u1ed9t l\u00e0m trong bao ng\u00e0y n\u1eefa th\u00ec xong con \u0111\u01b0\u1eddng.<br\/><b>\u0110\u00e1p s\u1ed1: <\/b> _input_(ng\u00e0y)","hint":"\u0110\u00e2y l\u00e0 b\u00e0i to\u00e1n n\u0103ng su\u1ea5t (l\u00e0m chung - l\u00e0m ri\u00eang) m\u00e0 kh\u1ed1i l\u01b0\u1ee3ng c\u00f4ng vi\u1ec7c kh\u00f4ng c\u1ee5 th\u1ec3 l\u00e0 bao nhi\u00eau n\u00ean ta coi vi\u1ec7c ho\u00e0n th\u00e0nh c\u00f4ng vi\u1ec7c l\u00e0 $1$ \u0111\u01a1n v\u1ecb.","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi th\u1eddi gian ho\u00e0n th\u00e0nh c\u1ee7a \u0111\u1ed9i m\u1ed9t l\u00e0 $x$<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n $1$ ng\u00e0y \u0111\u1ed9i m\u1ed9t l\u00e0m \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 3:<\/b> Bi\u1ec3u di\u1ec5n $1$ ng\u00e0y \u0111\u1ed9i hai l\u00e0m \u0111\u01b0\u1ee3c theo $x$ v\u00e0 t\u00ecm $10$ ng\u00e0y \u0111\u1ed9i hai l\u00e0m \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 4:<\/b> Bi\u1ec3u di\u1ec5n $28$ ng\u00e0y \u0111\u1ed9i m\u1ed9t l\u00e0m \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 5:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi th\u1eddi gian \u0111\u1ed9i m\u1ed9t l\u00e0m m\u1ed9t m\u00ecnh xong con \u0111\u01b0\u1eddng l\u00e0 $x$ (ng\u00e0y, $x\\in \\mathbb N^*, x > 20$)<br\/>M\u1ed9t ng\u00e0y \u0111\u1ed9i m\u1ed9t l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ (con \u0111\u01b0\u1eddng)<br\/>V\u00ec hai \u0111\u1ed9i c\u00f9ng l\u00e0m trong $20$ ng\u00e0y th\u00ec xong n\u00ean $1$ ng\u00e0y $2$ \u0111\u1ed9i l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {1}{20}$ (con \u0111\u01b0\u1eddng)<br\/>Suy ra, $4$ ng\u00e0y hai \u0111\u1ed9i l\u00e0m \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {4}{20}=\\dfrac {1}{5}$ (con \u0111\u01b0\u1eddng), m\u1ed9t ng\u00e0y \u0111\u1ed9i hai l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {1}{20}-\\dfrac {1}{x}$ (con \u0111\u01b0\u1eddng)<br\/>V\u1eady $10$ ng\u00e0y \u0111\u1ed9i hai l\u00e0m \u0111\u01b0\u1ee3c $10\\left(\\dfrac {1}{20}-\\dfrac {1}{x}\\right)=\\dfrac {1}{2}-\\dfrac {10}{x}$ (con \u0111\u01b0\u1eddng)<br\/>$28$ ng\u00e0y \u0111\u1ed9i $1$ l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {28}{x}$ (con \u0111\u01b0\u1eddng)<br\/>V\u00ec \u0111\u1ed9i m\u1ed9t tr\u1edf v\u1ec1 l\u00e0m ti\u1ebfp trong $28$ ng\u00e0y th\u00ec xong n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $\\dfrac {1}{5}+\\dfrac {1}{2}-\\dfrac {10}{x}+\\dfrac {28}{x}=1\\\\ \\Leftrightarrow \\dfrac {7}{10}-\\dfrac {10}{x}+\\dfrac {28}{x}=1\\\\ \\Leftrightarrow 7x-100+280=10x\\\\ \\Leftrightarrow 3x=180\\\\ \\Leftrightarrow x=60\\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$<br\/>V\u1eady \u0111\u1ed9i m\u1ed9t l\u00e0m m\u1ed9t m\u00ecnh trong $60$ ng\u00e0y th\u00ec s\u1eeda xong con \u0111\u01b0\u1eddng<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $60$<\/span><\/span>"}]}],"id_ques":979},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":"Hai ng\u01b0\u1eddi c\u00f9ng l\u00e0m chung m\u1ed9t c\u00f4ng vi\u1ec7c th\u00ec $3$ gi\u1edd $20$ ph\u00fat th\u00ec xong c\u00f4ng vi\u1ec7c. N\u1ebfu ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m m\u1ed9t m\u00ecnh trong $3$ gi\u1edd r\u1ed3i ng\u01b0\u1eddi th\u1ee9 $2$ l\u00e0m ti\u1ebfp m\u1ed9t m\u00ecnh trong $2$ gi\u1edd th\u00ec hai ng\u01b0\u1eddi l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {4}{5}$ c\u00f4ng vi\u1ec7c. H\u1ecfi ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m m\u1ed9t m\u00ecnh th\u00ec sau bao nhi\u1ec1u gi\u1edd th\u00ec xong c\u00f4ng vi\u1ec7c?","select":["A. $\\dfrac {3}{x}+\\dfrac {2}{x}=\\dfrac {4}{5}$","B. $\\dfrac {3}{x}+\\dfrac {3}{5}-\\dfrac {2}{x}=\\dfrac {4}{5}$","C. $\\dfrac {3}{x}+\\dfrac {20}{3}-\\dfrac {2}{x}=\\dfrac {4}{5}$","D. $\\dfrac {3}{x}+\\dfrac {3}{5}-\\dfrac {2}{x}=320$"],"hint":"","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi th\u1eddi gian ho\u00e0n th\u00e0nh c\u1ee7a \u0111\u1ed9i m\u1ed9t l\u00e0 $x$<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n $1$ gi\u1edd v\u00e0 $3$ gi\u1edd ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m \u0111\u01b0\u1ee3c theo $x$<br\/><b>B\u01b0\u1edbc 3:<\/b> Bi\u1ec3u di\u1ec5n $1$ gi\u1edd v\u00e0 $2$ gi\u1edd ng\u01b0\u1eddi th\u1ee9 hai l\u00e0m \u0111\u01b0\u1ee3c theo $x$ <br\/><b>B\u01b0\u1edbc 4:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi th\u1eddi gian ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m m\u1ed9t m\u00ecnh xong c\u00f4ng vi\u1ec7c l\u00e0 $x$ (gi\u1edd, $ x>\\dfrac {10}{3} $)<br\/>M\u1ed9t gi\u1edd ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ (c\u00f4ng vi\u1ec7c)<br\/>Suy ra $3$ gi\u1edd ng\u01b0\u1eddi th\u1ee9 nh\u1ea5t l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {3}{x}$ (c\u00f4ng vi\u1ec7c)<br\/>V\u00ec hai ng\u01b0\u1eddi c\u00f9ng l\u00e0m chung m\u1ed9t c\u00f4ng vi\u1ec7c th\u00ec $3$ gi\u1edd $20$ ph\u00fat $=\\dfrac {10}{3}$ gi\u1edd th\u00ec xong c\u00f4ng vi\u1ec7c n\u00ean $1$ gi\u1edd c\u1ea3 hai ng\u01b0\u1eddi l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {3}{10}$ (c\u00f4ng vi\u1ec7c)<br\/>V\u1eady $1$ gi\u1edd ng\u01b0\u1eddi th\u1ee9 hai l\u00e0m \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {3}{10}-\\dfrac {1}{x}$ (c\u00f4ng vi\u1ec7c)<br\/>V\u1eady $2$ gi\u1edd ng\u01b0\u1eddi th\u1ee9 hai l\u00e0m \u0111\u01b0\u1ee3c $2\\left(\\dfrac {3}{10}-\\dfrac {1}{x}\\right)=\\dfrac {3}{5}-\\dfrac {2}{x}$ (c\u00f4ng vi\u1ec7c)<br\/>V\u00ec hai ng\u01b0\u1eddi l\u00e0m \u0111\u01b0\u1ee3c $\\dfrac {4}{5}$ c\u00f4ng vi\u1ec7c n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $\\dfrac {3}{x}+\\dfrac {3}{5}-\\dfrac {2}{x}=\\dfrac {4}{5}$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 B<\/span><\/span>","column":2}]}],"id_ques":980}],"lesson":{"save":0,"level":2}}