multiples... arr..i hate them

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by Rahul@gurome » Thu Jan 20, 2011 2:47 am
Ramit88 wrote:If a, m and n are positive integers, is n^(2a) a multiple of m^2 ?

1. n is a multiple of m/2
2. n is a multiple of 2m
Statement 1: n is a multiple of m/2.
Hence, n^(2a) = (m/2)^(2a) = (m²/4)^a
Now, there may two possible cases,
  • 1. m has a single 2 in its prime factorization. Thus n has none. Hence n^(2a) is NOT a multiple of m^2.
    2. m has more than one 2 in its prime factorization. Thus n has at least one 2 in it. Hence n^(2a) may be a multiple of m^2.
Not sufficient

Statement 2: n is a multiple of 2m
Hence, n^(2a) = (2m)^(2a) = (4m²)^a = (m²)*[m^(2a - 2)]*[(4)^a]
a and m both being integer, we can conclude that n^(2a) is always a multiple of m^2.

Sufficient

The correct answer is B.
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