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# If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the

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If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the [#permalink]  12 Oct 2008, 13:38
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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

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.
[Reveal] Spoiler: OA
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Re: M02 Q25 Y value [#permalink]  12 Oct 2008, 14:53
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

Given is y=x+y meaning x=0

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

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.

again whats the source? cuz such questions are not of gmat type.

from i and ii cannot have 2 values for the same variable.
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Re: M02 Q25 Y value [#permalink]  12 Oct 2008, 18:51
y =x2-y2 /x-y => y =x+y

now y =x +y means x =0...

A:x=y=3 => 0+y =3 => y =3 ..sufficient

B:x-y=2 => 0-y =2 => y=-2...sufficient

IMO D:

Thanks
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SVP
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Re: M02 Q25 Y value [#permalink]  15 Oct 2008, 08:54
as long as x not = y

the expression boils down to

x+y = y ( only possible if x = 0), what is Y

from 1

X+Y = 3..........SUFF

FROM 2

X-Y = ...........SUFF

HOWEVER IN GMAT YOU WONT FIND SUCH A QUESTION ( Y CAN = 2 VALUES)
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Re: M02 Q25 Y value [#permalink]  16 Oct 2008, 04:34
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

Given is y=x+y meaning x=0

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

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.

In an arithmetic operator type question (e.g. y = 3, y = -2), I think there can be different values from two different statements for the answer to be D.

However, in a logical operator type question (is y positive, is y an integer), the two statements need to provide the same answer.

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Re: M02 Q25 Y value [#permalink]  23 Oct 2008, 06:08
Thanks, +1. We'll need to edit this question. Unfortunately, we still have some questions like this one. What do you say if we change S2 to x - y = -3?

Thanks.
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

Given is y=x+y meaning x=0

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

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.

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Re: M02 Q25 Y value [#permalink]  19 Sep 2010, 15:57
Thanks for the change (I'm seeing now how it would make better sense).

However, in simplifying the problem, you get y = [(x+y)(x-y)]/(x-y). Cross off the (x-y) in numerator and denominator, and you end up with: y = x+y.

Isn't this bad form? You can eliminate the y's on both sides and be left with an undefined solution.
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Re: M02 Q25 Y value [#permalink]  19 Sep 2010, 16:58
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NewSc2 wrote:
Thanks for the change (I'm seeing now how it would make better sense).

However, in simplifying the problem, you get y = [(x+y)(x-y)]/(x-y). Cross off the (x-y) in numerator and denominator, and you end up with: y = x+y.

Isn't this bad form? You can eliminate the y's on both sides and be left with an undefined solution.

It won't be "undefined solution": y=x+y --> y cancels out and you'll get x=0.
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Re: M02 Q25 Y value [#permalink]  21 Sep 2010, 01:00
Bunuel wrote:
NewSc2 wrote:
Thanks for the change (I'm seeing now how it would make better sense).

However, in simplifying the problem, you get y = [(x+y)(x-y)]/(x-y). Cross off the (x-y) in numerator and denominator, and you end up with: y = x+y.

Isn't this bad form? You can eliminate the y's on both sides and be left with an undefined solution.

It won't be "undefined solution": y=x+y --> y cancels out and you'll get x=0.

Gotcha. Dunno what I was thinking there.
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Re: M02 Q25 Y value [#permalink]  06 Nov 2010, 06:40
IMO -
Question was about finding unique value of Y.
When we simply the equation we get value of X, not Y,
Y = X + Y. thus, X = 0 but Y can be anything.

And 1 and 2 even though give different answers, but they do give solution to the question asked, thts value of Y.
So "D" sounds pretty correct.
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Re: M02 Q25 Y value [#permalink]  12 Nov 2010, 23:16
NewSc2 wrote:
Thanks for the change (I'm seeing now how it would make better sense).

However, in simplifying the problem, you get y = [(x+y)(x-y)]/(x-y). Cross off the (x-y) in numerator and denominator, and you end up with: y = x+y.

Isn't this bad form? You can eliminate the y's on both sides and be left with an undefined solution.

I think that makes the problem all the more easy.
Putting X=0 in both the statements gives us some a of Y (albeit different, but a value all the same).
D: Each statement alone is sufficient.

PS: Couple of days ago, I came across a question "Is (3x+7)/5 even?". If you think about it, all you have to do in this question is to find whether x is odd. Rephrasing the question sometimes makes it easy.
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Re: M02 Q25 Y value [#permalink]  12 Dec 2010, 19:32
D

As x = 0 so, both options are ok.

thanks
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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, 06:41
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

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.

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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, 10:43
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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.
Re: If y = \frac {x^2 - y^2}{x-y} ( x \ne y ), then what is the   [#permalink] 09 Nov 2012, 10:43
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