Is x>y^2? [1] x>y+5 [2] x^2-y^2=0 : DS Archive
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# Is x>y^2? [1] x>y+5 [2] x^2-y^2=0

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Is x>y^2? [1] x>y+5 [2] x^2-y^2=0 [#permalink]

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18 May 2007, 20:59
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I got this question from one of the GMAT Challenges: Is x>y^2?

[1] x>y+5
[2] x^2-y^2=0

The explanation makes sense up to a point. Clearly, stmt 1 is insufficient. Also, stmt 2 is insufficient. However, the explanation says that together they are sufficient because from stmt 2 we know that the |x|=|y| and putting this together with stmt 1 we know that x is positive and y is negative and neither is equal to zero. Then it says, "Therefore, x>y^2 is true." Here's my question:

How does that make x>y^2? If x is 2, then per stmt [1] y<-3. Let's say y=-4, then y^2=16. How can x>y^2 be true?

Any help is appreciated!

Thanks!
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18 May 2007, 21:11
From the reasoning you gave, x is positive and y is negative.

Now, to have x>y+5 and |x|=|y|, |x|>2.5

But in such cases, x can never be greater than y^2. So, together they are sufficient. Thanks for the correction, Himalayan

Last edited by mNeo on 18 May 2007, 21:49, edited 1 time in total.
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18 May 2007, 21:30
ans c is right. I agree with Himalayan's reasoning.

Last edited by CrackTheGmatInSFO on 18 May 2007, 21:49, edited 3 times in total.
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18 May 2007, 21:34
Bluebird wrote:
I got this question from one of the GMAT Challenges: Is x>y^2?

[1] x > (y+5)
[2] x^2 - y^2=0

The explanation makes sense up to a point. Clearly, stmt 1 is insufficient. Also, stmt 2 is insufficient. However, the explanation says that together they are sufficient because from stmt 2 we know that the |x|=|y| and putting this together with stmt 1 we know that x is positive and y is negative and neither is equal to zero. Then it says, "Therefore, x > y^2 is true." Here's my question:

How does that make x > y^2? If x is 2, then per stmt [1] y < -3. Let's say y = -4, then y^2=16. How can x > y^2 be true?

Any help is appreciated!

Thanks!

x = 2 and y = -4 are not correct.
only correct combination for x and y is x = -y and y is negative and less than -2.5

My version:
no dispute with A that it is insuff.

st. 2, if x = y= 5, x > y^2 is not true. if x = - y, then also not true. but x = y = 0.5, then it is true. so still insuff..

from i and ii, x = -y but y is smaller than -2.5. so in such condition, x > y^2 is not true.

therefore C makes sense.
Re: DS question   [#permalink] 18 May 2007, 21:34
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