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Wrong answer?

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Source: — Data Sufficiency |
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by vittalgmat » Thu Apr 16, 2009 12:34 pm
I think the explanation is wrong.
One cant assume the question to be the answer.
In the OA, the author assumes rs = rx - 2 and substitutes for rx, cancels rs blahblah. This is blatantly wrong!!!!.

The right way to solve is:
Pick either the RHS or LHS and derive the other side.

HT helps
-V
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by Ian Stewart » Thu Apr 16, 2009 4:38 pm
Yes, Vittal explains exactly what is wrong with the "solution" above. It's a great example of 'circular reasoning'. They assume the answer to the question is 'yes', and then prove the answer is 'yes'. Of course, that shouldn't come as a surprise!

Analyzing Statement 2 correctly, if x = s+2, then the right side of the equation in the question becomes r(s+2) - 2 = rs + 2r - 2. That will only be equal to rs if 2r - 2 = 0, or if r = 1. Since we don't know if r = 1, we can't be certain of the answer to the question, and the statement is insufficient. Combining Statements 1 and 2, it's still possible that r is 1, or that r is not 1, so the answer is E.

Out of curiosity, where is the question and 'solution' from?
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by hgiagiamou » Fri Apr 17, 2009 2:06 am
Ian Stewart wrote: Out of curiosity, where is the question and 'solution' from?

https://www.amazon.com/McGraw-Hills-GMAT ... 0071583327

Practice Test 3
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