Factor Problem

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DCJ: Senior | Next Rank: 100 Posts; Posts: 68; Joined: Mon May 04, 2009 10:01 pm

by DCJ » Sat Oct 17, 2009 8:21 pm

If 9 is a factor of 2X which of the following may not be and integer?

A. (6X/54)+(2X/3)
B. (4X-18)/9
C. (2X+27)/9
D. (81-4X^2)/81
E. (2X-3)/3

Ans: A

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Source: Beat The GMAT — Data Sufficiency | Sat Oct 17, 2009 8:21 pm

Talkativetree: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Tue Oct 13, 2009 3:31 pm

by Talkativetree » Sun Oct 18, 2009 6:12 pm

so from the Q stem, we know that 2x=9, 18, 27, etc.

so this means x is a multiple of 4.5.

we're looking for answers that will have an odd number of x's, because that is the only one that will result in a non-integer answer. simplifying the different answers will simplify into some form of 2x, which will result in an integer. looking at A. now,

(6X/54)+(2X/3)
X/9 + 2/3X

if x is 4.5, this will DEFINITELY be a non-integer answer.

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DCJ: Senior | Next Rank: 100 Posts; Posts: 68; Joined: Mon May 04, 2009 10:01 pm

by DCJ » Sun Oct 18, 2009 8:54 pm

O awesome. I assumed that X was an integer and therefore a multiple of 9. Thanks for clearing it up.

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