findmimi wrote:SAY A）READS SOMETHING LIKE
a=4 or a=5
And:
a=4 is sufficient while a=5 is not - Is A) considered to be sufficient?
Thanks,
P.S. when I say a=5 is not, that could mean
1) no solution for the question when a=5;
2) two or more solutions for the question when a=5.
Please advise.
Generally speaking, the situation you're describing is insufficient. A statement is sufficient if it allows only a single answer to the question stem. If your statement allows a to be both a 4 and a 5, and either one of these gives a different answer to the question stem, then the statement is insufficient, as it fails to lock down the answer to the question stem to a single answer.
Important caveat here, as I'm not sure what you mean by "no solution for the question": the GMAT DS questions are very unlikely to claim "no solution to the question" as grounds for insufficiency. It is far more likely that you are misinterpreting the implications of a=5: if a=5 means there's no solution to the question, then it is possible that a simply cannot equal 5 (i.e. 5 is not a valid plug in, since it contradicts something in the question stem), instead of it meaning that a=5 is insufficient.
I suggest that you post the question you have in mind, and we'll take a look at it.
