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Is xy > 0 ?

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Manager
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Joined: 11 Jan 2008
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Is xy > 0 ?  [#permalink]

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New post 02 Jan 2009, 20:11
Attachment:
vars.GIF
vars.GIF [ 1.67 KiB | Viewed 2480 times ]


can someone show how to do this by not plugging numbers..

also, what should be the approach for such pure variable q's.

Thanks

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Manager
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Joined: 28 Jul 2004
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Location: Melbourne
Schools: Yale SOM, Tuck, Ross, IESE, HEC, Johnson, Booth
Re: variables  [#permalink]

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New post 02 Jan 2009, 21:29
1
jackychamp wrote:
Attachment:
vars.GIF


can someone show how to do this by not plugging numbers..

also, what should be the approach for such pure variable q's.

Thanks


from (1) x > y-2 , x and y can be anything, hence not sufficient

from (2) x < 2y-6 , x and y can be anything, hence not sufficient

combine (1) and (2)

y-2 < x < 2y-6

or, y-2 < 2y-6
or, 2y-y > 6-2
or, y > 4

from (1) , since y > 4 ---> x > 4-2
or, x > 2

or, xy > 4.2 ---> xy > 8 ----> xy > 0 , hence (1) and (2) are sufficient and answer is (C)
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kris

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Re: variables  [#permalink]

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New post 02 Jan 2009, 22:12
yes, the OA is c.

thanks for the help.
Manager
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Re: variables  [#permalink]

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New post 06 Jan 2009, 20:45
solving the two equations is the way to go here.
x-y>-2
-x+2y>6
Thus, y>4 and x>2 and xy can be determined.

C
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Re: variables  [#permalink]

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New post 23 Jan 2009, 03:07
If you substitute for y>4 in the second inequality, you will not get x>2. Can someone explain please?

--== Message from GMAT Club Team ==--

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Re: variables &nbs [#permalink] 23 Jan 2009, 03:07
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