GMAT Guide book question

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Baldini: Senior | Next Rank: 100 Posts; Posts: 90; Joined: Mon Mar 02, 2009 6:06 am; Thanked: 3 times

by Baldini » Thu Mar 05, 2009 3:40 am

If y is an integer, is y^3 divisible by 9?
(1) y is divisible by 4
(2) y is divisible by 6

OA is B.

Could someone kindly explain the answer and the reasoning behind it?
Thx

GMAX

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Source: Beat The GMAT — Data Sufficiency | Thu Mar 05, 2009 3:40 am

bluementor: Master | Next Rank: 500 Posts; Posts: 418; Joined: Wed Jun 11, 2008 5:29 am; Thanked: 65 times

by bluementor » Thu Mar 05, 2009 4:10 am

Statement 1:

If y = 4, y^3 IS NOT divisible by 9
If y = 36, y^3 IS divisible by 9

Insufficient.

Statement 2:
If y is divisible by 6, this means y contains at least one factor of 3. Therefore, y^3 will contain at least 3 factors of 3 and will be divisible by 3^2.

Sufficient.

Choose B.

-BM-

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