Fastest Strategy to NP DS

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XLogic: Master | Next Rank: 500 Posts; Posts: 127; Joined: Sat Oct 02, 2010 8:55 am; Thanked: 17 times; Followed by:1 members

Fastest Strategy to NP DS

by XLogic » Fri Jan 28, 2011 11:18 pm

Hello,

I'm sure this is an easy question but I'm just starting out. I figured the right answer to the question (eventually) but it took too long to resolve. Please offer a fast strategy for these kinds of problems. Thanks.

QR 2nd Edition, Page 157:

64. If y is an integer, is y^3 divisible by 9?

(1) y is divisible by 4.
(2) y is divisible by 6.

Quote

Source: Beat The GMAT — Data Sufficiency | Fri Jan 28, 2011 11:18 pm

GMAT/MBA Expert

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pm; Location: Milpitas, CA; Thanked: 1854 times; Followed by:523 members; GMAT Score:770

by Anurag@Gurome » Sat Jan 29, 2011 12:31 am

XLogic wrote:If y is an integer, is yÂ³ divisible by 9?

(1) y is divisible by 4.
(2) y is divisible by 6.

If y is divisible by any positive multiple of 3, then yÂ³ will be divisible by 27 and hence by 9 too.

Statement 1: y may or may not be divisible by 3.

Not sufficient

Statement 2: y is divisible by 3. Hence yÂ³ is divisible by 9.

Sufficient

The correct answer is B.

Anurag Mairal, Ph.D., MBA
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