yes , you cant do like that

instead you can do
x/y = -1

x/y +1 =0

so (X+y) / Y =0

which is telling that X+y =0 we don't know the value of X-y

This is a poor quality question. I really doubt that it's from GMAT Prep.

From (1) we have that x + y = 8 and from (2) that x + y = 0. The statements contradict each other which cannot happen in proper GMAT question.

Topic locked.
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If x^2 = y^2, what is the value of x-y?

1) x+y = 8
2) x/y = -1

Dear Moderator,

This is a perfectly valid question. The fact that the two statements contradict each other implies that the combination of both should not be done. Therefore, we can advance that answers C and E are not possible.

What cannot happen in GMAT is that each statement is not sufficient and that when we combine both statements, they contradict each other. However, this is not the case in this question, so I do not understand why you have locked the previous topic with this question.

I would appreciate that you would let me share and discuss this question with all of you.

Thank you.

This is TOTALLY wrong. A book or a prep course which says otherwise is not of a high quality.

We have a discussion on this issue here: do-both-sufficient-statements-provide-the-same-answer-in-a-ds-question-135812.html
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