Students should keep working on problems until they think they understand all the ideas and can do all the sums correctly. For each candidate, this time could be different. There is no set time because it depends on the student. Students should make a plan for how they will study. Students should do sums every day, if possible, so they can keep doing them and be able to remember and use the information in the exam room. They should work on their math until they get it all right.