GMAT prepDS求解

luting0616 · 发表于 2015-9-19 23:41:18

Machine X and Y work at their respective constant rates. How many more hours does it take Machine Y, working alone, to fill a production order of a certain size than it takes Machine X, working alone?

1. Machine X and Y, working together, fill a production order of this size in two thirds the time that Machine X does.
2. Machine Y, working alone, fills a production order of this size in twice the time that Machine X, working alone, does.

guoyilin2015 · 发表于 2015-9-20 00:45:25

设完成某一单位工作，机器X用时x,机器Y用时y，求y-x
(1) X的效率为1/x，Y的效率为1/y，合力完成某一单位工作，需要用时1/(1/x+1/y)=2/3x，解得y=2x
(2) y=2x
(1)(2)等价，y-x=2x-x=x，x未知，E
如果给条件（1）和x就可解
OG上还有一道同开三台机器的，问同开两台需要多久。你可以看看

GMAT prepDS求解

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