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If x<=y and y = (x^2 - y^2)(x-y), then what is the value of

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If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  12 Oct 2008, 12:38
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If x\neq{y} and y = \frac{x^2 - y^2}{x-y}, then what is the value of y ?

(1) x+y-3=0
(2) x(y-3)=0

Source: GMAT Club Tests - hardest GMAT questions

Last edited by Bunuel on 07 Nov 2013, 01:13, edited 2 times in total.
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Kudos [?]: 36754 [0], given: 4532

Re: If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the [#permalink]  09 Nov 2012, 05:41
Expert's post
icandy wrote:
If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the value of y ?

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

[Reveal] Spoiler: OA
D

Source: GMAT Club Tests - hardest GMAT questions

Given is y=x+y meaning x=0

(1) says y=3 and (2) says y=-2

Given answer is D.

Isn't it one of the cardinal rules of GMAT that (1) and (2) do not contradict each other? Am I misinterpreting some thing here? The way I understood is if D were to be the answer for any DS Q, we should get the same value. If we are not getting such same answer, either we are doing some thing wrong or the Q itself is wrong.

Thoughts Fellas.

BELOW IS REVISED QUESTION OF THIS QUESTION:

If x\neq{y} and y = \frac{x^2 - y^2}{x-y}, then what is the value of y ?

y = \frac {x^2 - y^2}{x-y} --> y = \frac {(x - y)(x+y)}{x-y} --> y=x+y --> x=0.

(1) x+y-3=0 --> y=3. Sufficient.
(2) x(y-3)=0 --> since x=0 then y can take ANY value. Not sufficient.

Answer: A.
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Re: If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the [#permalink]  09 Nov 2012, 09:43
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Answer :D

Since both the options are independently sufficient to answer the question. (Value of y)

Although the value of y is not unique, if we get a solution for y it makes the option valid.
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  06 Nov 2013, 07:44
The OA to this question should be edited. I also got A but it said my answer was incorrect. Only realized once I read Bunuel's explanation.

OA still shows D.
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  06 Nov 2013, 09:15
Answer: A

Given: $y = \frac {x^2 - y^2}{x-y}$ = \frac{(x+y)(x-y)}{(x-y)}, which simplifies to y = x + y

Asked: What does y equal but is actually asking for x + y

1) Given: x + y = 3 --> insta-sufficient
2) Given: x - y = 2 --> insufficient since it tells us nothing about x + y

Therefore, A.

I'm really not sure why the OA says D....
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  06 Nov 2013, 16:41
Answer should be A.
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  06 Nov 2013, 21:10
I think the answer is D

From question y = x+y
1) x+y-3=0 ==> Since y = x+y ==> y-3=0 and y=3
2) x-y = 2 ==> x-(x+y) = 2 ==> x-x-y = 2 ==> -y=2 and y = 2

How X(y-3)=0 is obtained ?

Please help
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of [#permalink]  07 Nov 2013, 01:15
Expert's post
mhknair wrote:
I think the answer is D

From question y = x+y
1) x+y-3=0 ==> Since y = x+y ==> y-3=0 and y=3
2) x-y = 2 ==> x-(x+y) = 2 ==> x-x-y = 2 ==> -y=2 and y = 2

How X(y-3)=0 is obtained ?

Please help

The revised version of this question is here: if-x-y-and-y-x-2-y-2-x-y-then-what-is-the-value-of-71567.html#p1141701 and the OA is A.
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Re: If x<=y and y = (x^2 - y^2)(x-y), then what is the value of   [#permalink] 07 Nov 2013, 01:15
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