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Data sufficiency inequality question

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guy.b
 Post subject: Data sufficiency inequality question
 Post Posted: Sat Jul 31, 2010 3:29 am 
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Hi,
The DS question below is from MAN CAT exam. I didn't find it in another thread.

Is x·|y| > y^2?
(1) x > y
(2) y > 0

It is extremely tempting to divide both sides of this inequality by y or by the |y|, to come up with a rephrased question of “is x > y?” However, we do not know the sign of y, so this cannot be done.

I do not understand the explaination above.
why is ti wrong to divide both sides by |y| which is positive. Then, the question is equivalent to
Is x > |y|?
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sumedhagupta.iitd
 Post subject: Re: Data sufficiency inequality question
 Post Posted: Sat Jul 31, 2010 3:39 pm 
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You can divide any inequality by positive number.There is nothing wrong in that.
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guy.b
 Post subject: Re: Data sufficiency inequality question
 Post Posted: Sun Aug 01, 2010 10:23 am 
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So is there a mistake in the official answer given by Manhattan Gmat below?

It is extremely tempting to divide both sides of this inequality by y or by the |y|, to come up with a rephrased question of “is x > y?” However, we do not know the sign of y, so this cannot be done
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mschwrtz
 Post subject: Re: Data sufficiency inequality question
 Post Posted: Sun Aug 22, 2010 1:16 pm 
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No mistake, though apparently not quite clear enough.

What is y^2 divided by |y|?

If y>0, then |y|=y, so y^2 divided by |y|=y.

If y<0, then |y|=-y, so y^2 divided by |y|=-y.

Testing values will show that statement 1 is not sufficient, and so that simply dividing by |y| is wrong.

Is x·|y| > y^2?
(1) x > y

Suppose that y=-3 and x=2, then answer is no.
Suppose that y=1 and x=2, then answer is yes.
Not sufficient.
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yousuf_azim
 Post subject: Re: Data sufficiency inequality question
 Post Posted: Fri Sep 23, 2011 7:46 am 
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Students


Posts: 45
Dears,

What is the Ans?
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StaceyKoprince
 Post subject: Re: Data sufficiency inequality question
 Post Posted: Fri Nov 11, 2011 10:22 pm 
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Posts: 6064
Location: San Francisco
The answer is C.

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Stacey Koprince
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