If there is no penalty for guessing, then guess, but mark these questions so you can come back to them later and rethink your answer. Print your name on each sheet of paper or exam booklet you hand in. Return to your guesses and difficult questions and reread them. Check for clue words. Don't change a multiple choice answer unless you have a good reason to.
First responses tend to be more accurate.
Most exams in mathematics and physical science courses involve problems where you must apply the concept, knowledge, understanding, and techniques learned in the course to new situations. Here are some hints for problem solving exams. Do the easy ones first. Read the problem. Determine exactly what you are required to find.