pratk wrote:
Can someone please help me understand this. Is my approach correct?
If m is an integer, is m odd?
1. m/2 is not an even number
2. m-3 is an even number
My understanding is that each choice should not lead to a "Maybe" answer. But can it be sufficient if it leads to a "NO" or does it always have to be a "YES".
1. If we take m=10, the result is 5 which is not even. Therefore statement is sufficient in answering No m is not odd.
2. 5-3=2 which is even. Therefore statement 2 is sufficient because it also has a unique Yes answer that m is odd.
Thus the answer is D.
No, your approach is not quite right here. When you looked at Statement 1, you only picked one value for m, m=10. You will always get *some* answer to the question when you pick a value for m. Unfortunately that doesn't tell you much. If Statement 1 is sufficient, that means the answer must *always* be the same, for *every* value of m. So you can never only test one value in a DS question. Here, using Statement 1 alone, m could certainly be 10 and thus be even, but m could also be 11 and be odd. So we can get both a yes and a no answer using Statement 1, and it is not sufficient.
Statement 2 is sufficient, however, since if m - 3 is equal to an even number, then m is equal to an even number plus 3, so must be odd.
Finally, I'd add that in real GMAT questions, the two statements can never be inconsistent. If, in a yes/no DS question, each Statement is sufficient alone, they will both need to always give the same answer: either both will always give a yes answer or both will always give a no answer. If you think one statement always gives a yes answer and the other always gives a no answer, that's a certain sign that you've done something wrong.
_________________
GMAT Tutor in Montreal
If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com