$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 .\ $ $当\ x=3\ 时,\ y=-2 \times 3+7=1 .$ $ $ $解:设甲数为\ x , 乙数为\ y .\ $ $由题意, 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:设原两位数的十位上的数字是\ x , 个位上的数字是\ y .\ $ $根据题意, 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.\ \ $ $所以原两位数为 36.\ $ $ $ $解:设一台彩电的售价为\ x\ 元, 一台洗衣机的售价为\ y\ 元.\ $ $根据题意, 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:设该农户养鸡\ x\ 只, 养羊\ y\ 只.\ $ $根据题意, 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:设停车场有\ x\ 辆中型汽车,\ y\ 辆小型汽车.\ $ $根据题意, 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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