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DS Question??

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DS Question??

by rganesh » Wed Apr 09, 2008 1:56 pm
I'm stuck wondering why the answer is B and not D. Can someone explain why?
Is x2 equal to xy?
(1) x2 – y2 = (x + 5)(y - 5)
(2) x = y

I undersand the 2nd statement however, won't the answer to statement 1 be NO x2 does not equal xy and therefore it is sufficent because we are able to answer the Yes or No question?

I appreciate you assistance, maybe I am complicating things....
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Source: — Data Sufficiency |
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by Neo2000 » Wed Apr 09, 2008 9:55 pm
Umm how are you getting No from 1??

1 Equation , 2 unknowns => Cannot be solved. Nothing can be said from 1.

Atleast, i reasoned it that way. Am i missing something?
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Re: DS Question??

by Stuart@KaplanGMAT » Thu Apr 10, 2008 10:59 am
rganesh wrote:I'm stuck wondering why the answer is B and not D. Can someone explain why?
Is x2 equal to xy?
(1) x2 – y2 = (x + 5)(y - 5)
(2) x = y

I undersand the 2nd statement however, won't the answer to statement 1 be NO x2 does not equal xy and therefore it is sufficent because we are able to answer the Yes or No question?

I appreciate you assistance, maybe I am complicating things....
We can rewrite statement (1) as:

(x+y)(x-y) = (x+5)(y-5)

We're allowed to pick x=5 and y=5 (since (10)(0) = (10)(0)).
Is 5^2 = 5*5? YES.

We're also allowed to pick x=-5 and y=5 (since (0)(-10) = (0)(0)).
Is (-5)^2 = 5*(-5)? NO.

We can get both a "yes" and a "no", so (1) is insufficient.
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Thanks!

by rganesh » Fri Apr 11, 2008 8:26 am
That's exactly the explanation I was looking for!
Much appreciated.
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by humeixia » Fri Apr 11, 2008 3:53 pm
Yes, the answer is A.
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