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GMAT Prep: Probability

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GMAT Prep: Probability

by RM » Sat Jul 14, 2007 6:09 pm
If two the four expressions x+y,x+5y,x-y, and 5x-y are chosen at random, what is the probability that their product will be of the form of
sqr(x) - sqr(by), where b is an integer?

a. 1/2
b. 1/3
c. 1/4
d. 1/5
e. 1/6

answer is 1/6.
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by givemeanid » Sat Jul 14, 2007 6:13 pm
Two expressions out of four can be chosen in 4C2 = 6 different ways.
Product will be of the form x^2 - y^2 only when (x+y) and (x-y) are chosen.

So, probability = 1/6. Answer is E.
So It Goes
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