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第34頁(yè)

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

???$所以\frac {a}=\frac {11}{8}$???

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

???$所以x=2k，y=7k，z=5k$???

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

3:4

6

1:250000

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

9

???$解：(1)設(shè)a=4x，則b=3x，c=2x$???

???$因?yàn)閍+2b-3c=12$???

???$所以4x+2×3x- 3×2x= 12$???

???$解得，x=3$???

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

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

???$所以3(x-y)=2y$???

???$即x=\frac {5y}{3}$???

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

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