Is x an integer?

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Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pmFollowed by: 5 members; Thanked: 6 times

by Vincen » Wed Oct 11, 2017 6:38 pm

Is x an integer?

(1) x/3 is an integer
(2) 3x is an integer

The OA is A

Why statement (2) is not sufficient? And how can I prove, mathematically, that statement (1) is sufficient?

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Source: Beat The GMAT — Data Sufficiency | Wed Oct 11, 2017 6:38 pm

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Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 amFollowed by: 34 members; Location: Grand Central / New York; Thanked: 470 times

by Jay@ManhattanReview » Wed Oct 11, 2017 10:57 pm

Vincen wrote:Is x an integer?

(1) x/3 is an integer
(2) 3x is an integer

The OA is A

Why statement (2) is not sufficient? And how can I prove, mathematically, that statement (1) is sufficient?

Hi,

Statement 2 is not sufficient because @x = 1/3, 3x = 3*(1/3) = 1, an integer, so the answer is No; whereas @x = 1, 3x = 3*1 = 3, an integer, so the answer is Yes. No unique answer. Insufficient.

Hope this helps!

-Jay

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Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pmFollowed by: 5 members; Thanked: 6 times

by Vincen » Mon Oct 16, 2017 6:57 am

Thanks Jay.

But, What about statement (1)?

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