Tough Question from GMAT Prep

自由心证 · 发表于 2009-11-25 12:51:26

1. If two of the four expressions x+y, x+5y. x-y, and 5x-y are chosen at random, what is the probability that their product wil be of the form x^2-(by)^2，where b is an integer？

A. 1/2

B. 1/3

C. 1/4

D. 1/5

E. 1/6

sorry,这道题我没有答案，有没有nn知道怎么做啊？

doctortt · 发表于 2009-11-25 12:59:19

1 / C(4,2) = 1/6

It's testing you x^2 - y^2, so there is only one combination, which is (x+y) and (x-y)

x^2-(by)^2 is basically x^2 - y^2

自由心证 · 发表于 2009-11-28 06:30:59

Thanks!

Tough Question from GMAT Prep

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