GMATPrep: DS - Points in an XY plane : DS Archive
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# GMATPrep: DS - Points in an XY plane

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Manager
Joined: 31 Jul 2006
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GMATPrep: DS - Points in an XY plane [#permalink]

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20 Aug 2006, 21:41
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This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Please tell me the procedure to be followed in attacking this question..

Need to improve DS. Got Q50 on GMAT Prep, with 7 incorrects and all 7 were DS problems.

At one point of time I completely blacked out on this, picking numbers..

There was another post in which this problem was placed forward but no one got it correct, http://www.gmatclub.com/phpbb/viewtopic ... t=xy+plane

Will post the OA later..
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Senior Manager
Joined: 14 Aug 2006
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21 Aug 2006, 07:10
If (-a, b) and (-b, a) lie in the same quadrant then a and b should be both positive or negative

1. xy> 0 => implies x and y are either negative or positive
if positve (-x, y) in the II quad
if negative(x, -y) in the IV quad

INSUFF because there is no relationship between a,b and xy it can be either.

2. ax > 0 implies a and x are of the same sign. But we know nothing of y

if a and x are positive, the point can be either in the II quad or III quad (depending on whether Y is +ve or -ve)

INSUFF

Combined we know the sign of a = sign of x = sign of y

so C
Manager
Joined: 31 Jul 2006
Posts: 229
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Kudos [?]: 36 [0], given: 0

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21 Aug 2006, 08:50
Yup, thats the OA.
Thank you very much for the explanation.
You made it look very easy..

This is going straight to my log..
21 Aug 2006, 08:50
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