Unless there is some kind of trick I am not aware of, the answer will have to be devised by long division - all the way to the 4th number in order to accurately identify the solution. Not very typical for GMAT questions, since GMAC claims they are not testing our long division skills - rather our ability to find short exact ways to an answer.
Not necessarily, the GMAT definately uses approximations as a short cut (e.g 7.99854/3.98 is roughly 2). In this case, I think the little trick the question is using is to get us to identify that 23/12 is v. close to 24/12 = 2. There is only one choice that is just a touch under 2 so voila!
In the study cave!