megafan wrote:

If k is a multiple of 3 and \(k = (m^2)n\), where m and n are prime numbers, which of the following must be a multiple of 9?

(A) \(m^2\)

(B) \(n^2\)

(C) \(mn\)

(D) \(mn^2\)

(E) \((mn)^2\)

Source: Gmat Hacks 1800

must be a multiple of 9m and n are prime...lets have 2 and 3

now either of then can be a 3...

a) m can be 2 and n = 3...out

b) n can be 2 and m = 3...out

c) m = 2 and n=3 ...out

d) n can be 2 and m = 3...out

e) m = 2/3 or n = 3/2 both satisfies .......must be a multiple of 9

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