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GMAT Prep #2_PS Exponents #25

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by Anurag@Gurome » Sun Apr 01, 2012 7:21 pm
kwah wrote:Attached is a question from GMAT Prep Test #2.

What is the most efficient way of achieving the result?

Answer: D

Thanks,
K
4^17 - 2^28 = (2^2)^17 - 2^28 = 2^34 - 2^28 = (2^28)*(2^6 - 1) = (2^28)*(64 - 1) = (2^28)*63 = (2^28)*(3^2)*7

Hence, greatest prime factor of the given expression is 7.

The correct answer is D.
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