Q26:

Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y.  At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

A.      4

B.      6

C.      8

D.     10

E.      12

我的思路：设机器X的速度为a,机器Y的速度为b，得方程式

1）w/a=(w/b)+2

2)  5/4w/(a+b)=3

请问：我列的试子有问题吗？为什么解不出来呢！

E

1/(1/X)-1/(1/Y)=2

5/4/(1/X+1/Y)=3

得出:X=6,Y=4

2/(1/X)=12