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# Does x + c = y + c ? (1) x = y (2) x = c

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Re: Does x + c = y + c ? (1) x = y (2) x = c [#permalink]
racingip wrote:
The solution is supposed to be A. Yet, I am not clear about that.

My approach is as follows:

First, I simplify the equation: x+c=y+c, so I get x=y. The question becomes, is x=y?

Statement 1: x=y. Sufficient
Statement 2: x=c. Substituting x in the original equation we get x+x=y+x; 2x =y+x, and then x=y. So statement 2 is sufficient.

Solution is option D.

I am not sure what I am missing.

You're making the mistake of already assuming what you're attempting to prove either incorrect or correct in the problem. Be careful- this is a huge trap on data sufficiency; you can only reduce the equation in the stimulus to x=c if the stated equation x + c = y + c is already known to be true.
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Re: Does x + c = y + c ? (1) x = y (2) x = c [#permalink]
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(1) x=y, add C on both sides of the equation
x+c= y+c [Suff]
(2) x=c, if x=y then answer is yes

Kudos please if you like my explanation!
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Re: Does x + c = y + c ? (1) x = y (2) x = c [#permalink]
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racingip wrote:
Does x + c = y + c ?

(1) x = y
(2) x = c

Target question: Does x + c = y + c ?
This is a good candidate for rephrasing the target question.
Take the equation x + c = y + c, and subtract c from both sides to get: x = y

REPHRASED target question: Does x = y ?

Aside: the video below has tips on rephrasing the target question

Statement 1: x = y
Perfect!The answer to the REPHRASED target question is YES, x = y
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: x = c
Since we know nothing about the value of y, we cannot answer the REPHRASED target question
Statement 2 is NOT SUFFICIENT

Cheers,
Brent

RELATED VIDEO

Originally posted by BrentGMATPrepNow on 17 Apr 2019, 07:44.
Last edited by BrentGMATPrepNow on 17 May 2021, 07:26, edited 1 time in total.
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Re: Does x + c = y + c ? (1) x = y (2) x = c [#permalink]
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Re: Does x + c = y + c ? (1) x = y (2) x = c [#permalink]
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