agganitk wrote:Hi andrea,
What about the word sometimes in option D ? Why have you ignored it? Please explain

grockit_andrea wrote:

duongthang wrote:D is correct but D use formal logic IF A THEN B, IF NOT B THEN NOT A

formal logic is not tested on GMAT though it is tested on LSAT.

I think we should not study this question.

Duongthang, I've seen several posts by you in which you say that formal logic is not tested on the GMAT and should therefore not be studied. While knowledge of formal logic isn't necessary on the GMAT, I firmly believe that it will help on many questions in the critical reasoning section; the linear thinking that is promoted by formal logic can help test-takers understand some of the reasoning on the GMAT, particularly in terms of inferences or assumptions. For instance (I'm sure this is neither the best example nor the only example, but it's illustrative and it also happens to be on the page I was just looking at) both OG 12 CR 20 and OG 12 CR 33 can absolutely be solved using the principles of formal logic.

The GMAT isn't designed to require formal logic, and if you don't find it helpful, then of course it's not worthwhile for you to study it. But it's helpful to many people, and since there are questions on the test that can be understood using it, I think it's great for people who are interested to gain an understanding of it.