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GMAT Prep #2_PS Probability #14

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by Anurag@Gurome » Sun Apr 01, 2012 7:13 pm
kwah wrote:Attached is a question from GMAT Prep Test #2.

What is the most efficient way of achieving the result?

Answer: E

Thanks,
K
The pairing of given four expressions can be done in 4C2 = 4!/2!2! = 6 ways
x² - (by)² = (x - by)(x + by), and out of the given expressions, only one pair us making such expression, [x + (1 * y)][x - (1 * y)], whose probability is [spoiler]1/6[/spoiler].

The correct answer is E.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
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