gmat prep question

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gmat prep question

by yvonne12 » Mon May 28, 2007 3:07 pm
is xy>0

1. x-y>-2
2. x-2y<-6

please explain

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Re: gmat prep question

by jayhawk2001 » Mon May 28, 2007 6:45 pm
yvonne12 wrote:is xy>0

1. x-y>-2
2. x-2y<-6

please explain
Is it C?

1 - insufficient. Take x = 5, y= 3 and x = 5, y = -3. xy can be positive
or negative.

2 - insufficient. Take x = 5, y = 6 and x = -5, y = 6. xy can be positive
or negative.

Together,

x > y-2 & x < 2y-6

y-2 < x < 2y-6

We can see that the above falls apart for all values y < 4 and x < 2.
So, x and y have to be positive and hence C.

Alternatively, I think we can do the following

x-y > -2
2y-x > 6

Adding, we get y > 4. And so x > 2. Hence sufficient and so C.

OA please.