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MGMAT (Guide 3 pg. 136) Example question.

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Senior | Next Rank: 100 Posts
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by OneTwoThreeFour » Fri Feb 18, 2011 7:55 pm
Is xy = -1?

(1) x=y
(2) y=1

The correct answer is [spoiler] A. Either I am legally retarded or there is a mistake in the question. Why isn't (2) also correct? If y=1, then x(1) =-1. So x has to be -1. Therefore, xy = (-1)(1)= -1. Help me out here[/spoiler]
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Source: — Data Sufficiency |
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by Pilot » Fri Feb 18, 2011 9:14 pm
My answer is A.
1. Sufficient. If x=y, then xy is non negative. xy is not equal to -1.
2. Insufficient. x=0, y=1 ; x=-1, y=1.
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by OneTwoThreeFour » Fri Feb 18, 2011 10:36 pm
Just realized what I did wrong. For (2), when y is -1 the question becomes does x=-1? Guess I gotta keep things in perspective and focus on the question rather than jump right away into the conclusion.
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