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If x-y > 10, is x-y > x+y ?

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alysekilleen
 Post subject: If x-y > 10, is x-y > x+y ?
 Post Posted: Sat Aug 14, 2010 10:11 pm 
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Course Students


Posts: 6
If x-y > 10, is x-y > x+y ?

1) x = 8

2) y = -20

This is a data sufficiency question.

The correct answer is d.

An explanation from an instructor would be much appreciated.

Best,
Alyse
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gokul_nair1984
 Post subject: Re: If x-y > 10, is x-y > x+y ?
 Post Posted: Sat Aug 14, 2010 11:21 pm 
Offline
Students


Posts: 170
Hi there.. I'm not an instructor but will try to explain this stuff..

If x-y > 10, is x-y > x+y ?

First of all rephrase the stem...x-y>x+y...=>-y>y..That means we just have to check if y is negative as only the negative of a negative number will be positive.

Case 1: x = 8(Given)

This means y>-2....Hence Sufficient

Case 2: y = -20...this again is Self Sufficient

Hence the option is D
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RonPurewal
 Post subject: Re: If x-y > 10, is x-y > x+y ?
 Post Posted: Thu Aug 26, 2010 8:48 am 
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ManhattanGMAT Staff


Posts: 6765
gokul, nice solution.

i guess we should probably elaborate on this:

gokul_nair1984 wrote:
Case 1: x = 8(Given)

This means y>-2....Hence Sufficient


this comes from plugging x = 8 back into the original inequality from the prompt (x - y > 10).
that gives
8 - y > 10
-y > 2
divide by -1 (don't forget to flip around the ">") to give
y < -2

therefore, y is negative.
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