number properties

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Source: — Data Sufficiency |

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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.
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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