How many exams have you over-studied for? It seems worth asking. Obviously some do slide by. But I think far more degree completers study more than they have to, if only to be confident of the result, although obviously sometimes the pressure of a deadline causes the serious student just to cut things short! --Orson
A tough question to answer - if "over-studying" means that I achieved a much higher grade than I needed to get an "A", then I'd say all of them. However, as you say, I wanted to have a comfortable margin to ensure I got an "A"; in this case I'd say I studied about as much as I needed to.