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第34頁

信息發(fā)布者：

$???解：(1)因為\frac {a-b}=\frac {a}-1=\frac {3}{8}???$

$???所以\frac {a}=\frac {11}{8}???$

???$解：(2)\frac {x}{2}=\frac {y}{7}=\frac {z}{5}=k(k≠0)$???

???$所以x=2k，y=7k，z=5k$???

???$所以\frac {x+y-z}{x}=\frac {2k+7k-5k}{2k}=2$???

3:4

6

1:250000

???$\frac {1}{3}$???

$???\frac {1}{3}???$

9

$???解：(1)設(shè)a=4x，則b=3x，c=2x???$

$???因為a+2b-3c=12???$

$???所以4x+2×3x- 3×2x= 12???$

$???解得，x=3???$

$???c= 2x= 6???$

$解：(2)因為\frac {x-y}{y}=\frac {2}{3}??????$

$所以3(x-y)=2y$

$??????即x=\frac {5y}{3}$

$??????所以原式=\frac {2×\frac {5y}{3}+5y}{3×\frac {5y}{3}-y}=\frac {25}{12}???$

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