書寫求救!!!!!!!!!!

chasechase12

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 times that machine X working alone does.

(2) machine y working alone, fills a production order of this size in twice the time that machine X, working alone does.

ANS: E

nafegogo

要求的是：
(1/x)-1/（x+y)=y/（x+y)
根据楼上的第一个条件 只能求出是多少1/x  不知道x 不行
第二个条件 能推出x:y
为什么我觉得应该选B？？？

chasechase12

why E??

NoDoubt88

(1/x)*2/3=1/(x+y)

(1/x)*2=1/y