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Source: — Data Sufficiency |

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by Jay@ManhattanReview » Fri Oct 27, 2017 9:32 pm
LUANDATO wrote:x and y are two positive integers. D is the greatest common divisor of x and y. Is D > 20?

(1) x is a multiple of 4

(2) y is a multiple of 20

The OA is E.

I don't understand it. Can any expert explain this DS question for me please? Thanks.
(1) x is a multiple of 4

Given x is a multiple of 4, x can be 4, 8, 12, 16, 20, 24, 28, 32, 36, 40...etc. Moreover, we do not have information about y. Insufficient.

(2) y is a multiple of 20

y can be 20, 40, 80, etc. Moreover, we do not have information about x. Insufficient.

(1) and (2) combined:

Case 1: If x = 4 and y = 20, then GCD = 4.
Case 2: If x = 20 and y = 20, then GCD = 20. No unique answer.

Insufficient.

The correct answer: E

Hope this helps!

-Jay

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