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Source: — Data Sufficiency |
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by GmatMathPro » Fri Sep 30, 2011 11:36 pm
A useful thing to keep in mind on problems like these is that every prime number besides 2 is odd.

Statement 1: If M is prime, it is either 2 or some odd prime. It can't be 2 because M+7 would then be 9, which is not prime. If M is an odd prime, then M+7 is odd+odd which is always even and greater than 2, and would not be prime. Therefore, M cannot be prime if M+7 is prime. SUFFICIENT

Statement 2: Similar reasoning. M can't be 2 again, because that would make M-7=-5, and M can't be an odd prime because that would make M-7 an even number that is not 2. Therefore, M cannot be prime if M-7 is prime.

So the answer is D
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by olylo » Sat Oct 01, 2011 12:28 pm
Thank you so much for solving the question.
Your explanation is very clear.

Thanks again
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