?$解:由已 知, 得\ \left\{\begin{array}{l}k+b=5, \\ -2 k+b=11 .\end{array}\right.\ 解得\ \left\{\begin{array}{l}k=-2, \\ b=7 .\end{array}\right.\ \ $? ?$所以\ y=-2 x+7 .\ $? ?$當(dāng)\ x=3\ 時,\ y=-2 \times 3+7=1 .$? ?$ $? ?$解:設(shè)甲數(shù)為\ x , 乙數(shù)為\ y .\ $? ?$由題意, 得\ \left\{\begin{array}{l}2 x-y=4, \\ 4 x=3 y .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=6, \\ y=8 .\end{array}\right.\ $? ?$ $? ?$解:設(shè)原兩位數(shù)的十位上的數(shù)字是\ x , 個位上的數(shù)字是\ y .\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}x+y=9, \\ 10 x+y+27=10 y+x .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=3, \\ y=6 .\end{array}\right.\ \ $? ?$所以原兩位數(shù)為 36.\ $? ?$ $? ?$解:設(shè)一臺彩電的售價為\ x\ 元, 一臺洗衣機的售價為\ y\ 元.\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}x-y=1000, \\ 13 \%(x+y)=390 .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=2000, \\ y=1000 .\end{array}\right.\ $? ?$ $? ?$ $? ?$解:設(shè)該農(nóng)戶養(yǎng)雞\ x\ 只, 養(yǎng)羊\ y\ 只.\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}x+y=40, \\ 2 x+4 y=136 .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=12 \text {, } \\ y=28 .\end{array}\right.\ $? ?$ $? ?$ $? ?$解:設(shè)停車場有\(zhòng) x\ 輛中型汽車,\ y\ 輛小型汽車.\ $? ?$根據(jù)題意, 得\ \left\{\begin{array}{l}x+y=50, \\ 6 x+4 y=230 .\end{array}\right.\ 解得\ \left\{\begin{array}{l}x=15, \\ y=35 .\end{array}\right.\ $? ?$ $? ?$ $?
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