If n and y are positive integers and 450y=n^3, which of the following must be an integer?

I. y/3∗2^2∗5

II. y/3^2∗2∗5

III. y/3∗2∗5^2

A. None.

B. I only.

C. II only.

D. III only.

E. I, II, and III

Correct Answer: B

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This is one of the most difficult questions in the GMAT universe. That said, there is a simple way to solve it that relies on a fundamental divisibility rule every GMAT studier should know:

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