解:由①得???$，y-1=\frac {3}{2}(x-1)③$??? 把③代入②得???$，6(x-1)=3(x+5) $??? ∴???$x=7 $??? ???$\text { 把 } x=7 \text { 代入(1)得, } 18=2(y-1) $??? ∴???$y=10$??? 所以方程組的解為???$\begin {cases}{x=7 }\\{y=10}\end {cases}$???
?$解:設(shè)第一種書的原價為\ x\ 元, 第二種書的原價為\ y\ 元.\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}x+y=880, \\ (1-80 \%) x+(1-75 \%) y=200 .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=400, \\ y=480 .\end{array}\right.\ $? ?$ $? ?$ $? ?$解:設(shè)原長方形的長為\ x \mathrm{~cm}\ 、寬為\ y \mathrm{~cm} .\ $? ?$由題意, 得\ \left\{\begin{array}{l}x-4=y+2, \\ (x-4)(y+2)=x y,\end{array}\right.\ 即\ \left\{\begin{array}{l}x-4=y+2, \\ 2(x-4)=4 y .\end{array}\right.$? ?$解得\ \left\{\begin{array}{l}x=8, \\ y=2 .\end{array}\right.\ \ $? ?$ $? ?$ $? ?$解:設(shè)\ \mathrm{A}\ 種帳篷\ x\ 頂,\ \mathrm{B}\ 種帳篷\ y\ 頂.\ $? ?$根據(jù)題意,列方程組\ \left\{\begin{array}{l}x+y=600, \\ 1700 x+1300 y=940000 .\end{array}\right.\ \ $? ?$解得\ \left\{\begin{array}{l}x=400, \\ y=200 .\end{array}\right.\ \ $? ?$ $? ?$ $? ?$解:設(shè)這個班共有\(zhòng) x\ 名同學(xué), 這批任務(wù)共需\ y\ 朵小紅花.\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}y+20=20 x, \\ y-31=19 x .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=51, \\ y=1000 .\end{array}\right.\ $? ?$ $? ?$ $? 解:①+②得?$4x=6，$? ∴?$x=\frac 32，$? 把?$x=\frac 32$?代入②得 ?$3-y=1，$? ∴?$y=2，$? ∴方程組的解為?$\begin {cases}{x=\frac 32}\\{y=2}\end {cases}$?
解:②-①得?$5m=-10，$? ∴?$m=-2，$? 把?$m=-2$?代入①得: ?$-2+2n=9，$? ∴?$n=\frac {11}{2}，$? ∴方程組的解為?$\begin {cases}{m=-2，}\\{n=\frac {11}{2}}\end {cases}$?
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