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number properties

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Source: — Data Sufficiency |

by Anurag@Gurome » Fri Jan 20, 2012 12:23 am
sud21 wrote:m and n are integers, is m^n an integer?
1) n^m is positive
2) n^m is an integer
(1) n^m is positive.
If n = -2, m = 2, then n^m = (-2)^2 = 4 and m^n = 2^(-2) = 1/2² = 1/4 = 0.25, not an integer.
If n = 2, m = 2, then n^m = (2)^2 = 4 and m^n = 2^(2) = 4, an integer.
No definite answer; NOT sufficient.

(2) n^m is an integer.
If n = -2, m = 3, then n^m = (-2)^3 = -8 and m^n = 2^(-3) = 1/(2^3) = 1/8 = 0.125, not an integer.
If n = 2, m = 2, then n^m = (2)^2 = 4 and m^n = 2^(2) = 4, an integer.
No definite answer; NOT sufficient.

Combining (1) and (2), n^m is a positive integer. Taking the same examples as in statement 1, again it is NOT sufficient.

The correct answer is E.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

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by rijul007 » Fri Jan 20, 2012 1:06 am
sud21 wrote:m and n are integers, is m^n an integer?
1) n^m is positive
2) n^m is an integer
The ques can be rephrased as:
Is n positive?


1) n^m is positive
we cant say ..
n could be positive or negative..

Insufficient


2) n^m is an integer
cant say
this tells us that m is positive.. but tells us nothing about n
Insufficient


Combining the two statements
Still insufficient


Option E
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