Is xy > 0 ? (1) x-y > -2 (2) x - 2y < -6 : DS Archive
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# Is xy > 0 ? (1) x-y > -2 (2) x - 2y < -6

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Is xy > 0 ? (1) x-y > -2 (2) x - 2y < -6 [#permalink]

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02 Aug 2007, 07:41
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Is xy > 0 ?

(1) x-y > -2
(2) x - 2y < -6
VP
Joined: 10 Jun 2007
Posts: 1459
Followers: 7

Kudos [?]: 255 [0], given: 0

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02 Aug 2007, 08:13
sumande wrote:
Is xy > 0 ?

(1) x-y > -2
(2) x - 2y < -6

Got C, what's OA?

xy>0 when both positive or both negative
(1) x-y > -2
Doesn't tell us anything. Say x=5, y=6, this works!
Say x=-4, y = 3, this also works.
INSUFFICIENT

(2) x-2y <-6
Say y =2, x=-4, works!
Say y=10, x=1 works!
INSUFFICIENT

Together, we can reduce to one equation by inequalities addition rule.
1) x-y > -2
2) -x+2y > 6
We get y>4.
Test y with equation 1)
x-y>-2, if y>4, this means that x will always be positive
I don't think I have to test this with equation 2) since we already know from 1) that x will always be positive.
Senior Manager
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02 Aug 2007, 09:51
Thanks guys! OA is C.
The addition of inequalities slipped my mind.
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02 Aug 2007, 22:29
St1:
Insufficient. Both x and y can be 0, or Both x and y can be -1/2.

St2:
x can be 1, y can be 10 then x-2y<6>0)
x can be -20, y = 1, then x-2y<-6 and xy = -20.(<0> -2
-x+2y > 6

Then y>4. If y is greater than 4, then x must be greater than y. And xy > 0. Sufficient,
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03 Aug 2007, 00:12
bkk145 wrote:
sumande wrote:
Is xy > 0 ?

(1) x-y > -2
(2) x - 2y < -6

Got C, what's OA?

xy>0 when both positive or both negative
(1) x-y > -2
Doesn't tell us anything. Say x=5, y=6, this works!
Say x=-4, y = 3, this also works.
INSUFFICIENT

(2) x-2y <-6
Say y =2, x=-4, works!
Say y=10, x=1 works!
INSUFFICIENT

Together, we can reduce to one equation by inequalities addition rule.
1) x-y > -2
2) -x+2y > 6
We get y>4.
Test y with equation 1)
x-y>-2, if y>4, this means that x will always be positive
I don't think I have to test this with equation 2) since we already know from 1) that x will always be positive.

Perfect !

Re: DS : GMATPrep   [#permalink] 03 Aug 2007, 00:12
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