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If y = (x^2 - y^2)/(x-y) (x y ), then what is the value of y [#permalink]

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16 Oct 2011, 04:07

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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. \(x - y = -3\)

(C) 2008 GMAT Club - m02#25

Hi All-

I'm struggling to see the logic behind the OA in this question. Taking the information from the question stem, we get y= (x+y)(x-y)/ (x-y), therefore y=x+y. Its easy to see that statement 1 is sufficient, but for statement 2, we will still get y=x+y because y=-3(x+y)/-3. We can pick a number of different values for x-y that equal -3 that fit the question stem (x is not equal to y). Can someone with better math skills than myself explain why statement 2 is sufficient? Cheers!

Re: If y = (x^2 - y^2)/(x-y) (x y ), then what is the value of y [#permalink]

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16 Oct 2011, 04:14

1

This post received KUDOS

kenman 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. \(x - y = -3\)

(C) 2008 GMAT Club - m02#25

Hi All-

I'm struggling to see the logic behind the OA in this question. Taking the information from the question stem, we get y= (x+y)(x-y)/ (x-y), therefore y=x+y. Its easy to see that statement 1 is sufficient, but for statement 2, we will still get y=x+y because y=-3(x+y)/-3. We can pick a number of different values for x-y that equal -3 that fit the question stem (x is not equal to y). Can someone with better math skills than myself explain why statement 2 is sufficient? Cheers!

-Ken

Mark my words bro, if you follow the way you are solving the questions you will face a difficult time with DS questions. Always simply the equations till end, else you will complicate the things for you... - GOLDEN RULE.

now when you got y =x+y => x must be 0 now when you will put x=0 in both the statements you will have unique value of Y. => both are sufficient.

Now spend at least 15-20 mins on the advice I gave you and try to put in every question. Always simplify and then go ahead.
_________________

Re: If y = (x^2 - y^2)/(x-y) (x y ), then what is the value of y [#permalink]

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16 Dec 2011, 07:07

Excellent question kenman. Definitely worth another look. Its easy to miss out on the minor details and make careless mistakes as I did. D is the right answer. Thanks for the explanation gurpreetsingh. Kudos to both..
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Re: If y = (x^2 - y^2)/(x-y) (x y ), then what is the value of y [#permalink]

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06 Feb 2015, 17:14

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Re: If y = (x^2 - y^2)/(x-y) (x y ), then what is the value of y [#permalink]

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30 Aug 2016, 08:02

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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