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Fraction problem

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gmatmba
 Post subject: Fraction problem
 Post Posted: Fri Apr 18, 2008 5:43 pm 
If y = (x^2 - y^2 ) / x-y, then what is the value of y?

1. x + y = 3
2. x - y = 2

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient
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Sudhan
 Post subject:
 Post Posted: Fri Apr 18, 2008 7:25 pm 
Y=(X^2-Y^2)/X-Y
= (X-Y) (X+Y)/X-Y
= X+Y

Y=X+Y WHICH MEANS X=0

We can rephrase the question as Is X=0?

AD
BCE Grid

A) Talk about Y which is not needed INSUFF
B) Talk about Y which is not needed INSUFF
Combining A & B we get

x+y=3
x-y=2

Solving for X we get x=5/2

From this we can say C is sufficient to answer the question.

Hope it helps.
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RonPurewal
 Post subject:
 Post Posted: Fri Apr 18, 2008 9:33 pm 
Offline
ManhattanGMAT Staff


Posts: 7146
you need to post a source for this problem. please do so in the next couple of days, or else we'll have to delete the thread.

thank you.
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gmatstudent
 Post subject: Fractions-Princeton Review
 Post Posted: Mon Apr 21, 2008 11:21 am 
Ron, the source of the problem is above.

Thank you
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RonPurewal
 Post subject: Re: *Fraction problem
 Post Posted: Wed Apr 23, 2008 4:38 am 
Offline
ManhattanGMAT Staff


Posts: 7146
gmatmba wrote:
If y = (x^2 - y^2 ) / x-y, then what is the value of y?

1. x + y = 3
2. x - y = 2

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient


are you sure you've posted this question correctly?

as another poster said, you can rephrase the original statement to y = x + y, which means that x = 0. so, we have: 'if x = 0, then what is the value of y?'
technically, either (1) or (2) is sufficient, because (1) says 0 + y = 3, and (2) says 0 - y = 2. but that's where we run into problems: we have 2 statements that contradict each other, a situation that's strictly not allowed on the real test.

worse yet, if you take the two statements together, you can solve them as simultaneous equations, yielding x = 2.5 and y = 0.5. but then (x^2-y^2)/(x-y) is 6/2 = 3, which definitely doesn't equal y.

something is wrong in problemville.

but wait - you didn't include parentheses around x-y in the original. are you saying it's actually the fraction (x^2 - y^2) divided by JUST x, and then that fraction minus y? because that would be a whole different ballgame. if so, just post to that effect.
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