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gmat prep data sufficiency

This topic has 2 member replies
djsir007 Junior | Next Rank: 30 Posts Default Avatar
Joined
15 Apr 2007
Posted:
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gmat prep data sufficiency

Post Wed Apr 18, 2007 3:50 pm
if ab does not = 0, and points (-a,b)(-b,a) are in the same quadrant of the xy plane, is point (-x,y) in the same quadrant?
(1) xy>0
(2) ax>0

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Prasanna Master | Next Rank: 500 Posts
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Post Fri Apr 20, 2007 6:12 am
Think the answer is C

My approach was as under:

The problem states that (-a,b)(-b,a) are in the same xy plane. This can be true only when in cases where

- Both a and b have a positive value or
- Both a and b have a negative value

(given that ab is not equal to zero)

With this information we can use (2) which says ax>0. This means that x retains the sign of a. If a is a positive value, then x is positive and if a is negative, x is negative to make ax>0.

Now (1) tells us that xy>0 and hence y retains the sign of x.

Hence for any set of values for a and b (fulfilling the above 2 conditions)
(-x,y) would be in the same quadrant as (-a,b)(-b,a).

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gabriel Legendary Member
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Post Fri Apr 20, 2007 9:26 am
Prasanna wrote:
Think the answer is C

My approach was as under:

The problem states that (-a,b)(-b,a) are in the same xy plane. This can be true only when in cases where

- Both a and b have a positive value or
- Both a and b have a negative value

(given that ab is not equal to zero)

With this information we can use (2) which says ax>0. This means that x retains the sign of a. If a is a positive value, then x is positive and if a is negative, x is negative to make ax>0.

Now (1) tells us that xy>0 and hence y retains the sign of x.

Hence for any set of values for a and b (fulfilling the above 2 conditions)
(-x,y) would be in the same quadrant as (-a,b)(-b,a).
excellent attempt ... me to getting the answer as C ...

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