If time is an issue, just skip the question. Typically, you can tell if you are really going to have to work at it to arrive at a correct answer. And if you feel it is going to take 2+ minutes to come to an answer, just come back to it later. I have found that this technique has helped me finish with 7-10 minutes left to really work out the hard questions. If you try to finish the hard ones as they come, you will not get to the easy ones at the end. So even if you cannot get back to all of the hard ones, at least you will be able to answer the easy ones you would have not gotten to otherwise.