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by gmatblood » Fri Nov 04, 2011 10:53 am
If n is a positive integer,is the value of b-a at least twice the value of 3^n - 2^n
(1) a = 2^n+1 and b=3^n+1
(2) n =3

IMO: A
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Source: — Data Sufficiency |
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by neelgandham » Fri Nov 04, 2011 11:08 am
If n is a positive integer,is the value of b-a at least twice the value of 3^n - 2^n
(1) a = 2^n+1 and b=3^n+1 => b-a = 3^n-2^n, Sufficient
(2) n =3 Insufficient

IMO A
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by Anurag@Gurome » Fri Nov 04, 2011 10:55 pm
gmatblood wrote:If n is a positive integer,is the value of b-a at least twice the value of 3^n - 2^n
(1) a = 2^n+1 and b=3^n+1
(2) n =3

IMO: A
(1) a = 2^(n+1) and b = 3^(n+1) implies we have to find if 3^(n+1) - 2^(n+1) > 2*(3^n - 2^n)? or is 3 * 3^n - 2 * 2^n > 2 * 3^n - 2 * 2^n?
We get, 3*3^n > 2*3^n, which is clearly true. So, statement 1 is SUFFICIENT.

(2) n = 2 is clearly NOT sufficient to answer the question.

The correct answer is A.
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