Multiples Challenge

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jeffboshine: Junior | Next Rank: 30 Posts; Posts: 19; Joined: Tue Feb 09, 2010 8:31 am; Thanked: 1 times

by jeffboshine » Thu Mar 29, 2012 4:36 pm

If the question stem states that X^2 is a multiple of 64, can we simplofy that to X is a multiple of 8?

I say no, what do you think?

Also, is there an easy way to simplify that part of the stem?

Thanks

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Source: Beat The GMAT — Data Sufficiency | Thu Mar 29, 2012 4:36 pm

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Thu Mar 29, 2012 5:21 pm

jeffboshine wrote:If the question stem states that X^2 is a multiple of 64, can we simplofy that to X is a multiple of 8?

I say no, what do you think?

Also, is there an easy way to simplify that part of the stem?

Thanks

You're right. If x^2 is a multiple of 64, we cannot conclude that x is a multiple of 8.

For example if x = root(132) then x is not a multiple of 8.
However, since [root(32)]^2 = 132, we can see that x^2 is a multiple of 64.

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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