When I'm left with very little time and a lot of questions to do what I do is solve every alternate question or guess on every alternate question, depending on how you look at it. I came across this strategy in one of the Aristotle Prep books and I find this extremely useful as it gives me more time to do each question and also reduces the probability of my getting all or most of these questions wrong. Though, I agree, the ideal situation is to not end up with such a situation in the first place by managing your time effectively on the test, something that is easier said than done.