In the last 24 to 48 hours prior to a test you should have already covered every subject there is to cover that is believed to be on the test. Within those hours you should be focusing on the problems that you didn't know in the beginning of your preparation and just recapping that you understood everything you have preciously studied. You should not study very hard as to hurting your brain and over studying that you confuse yourself test day. You should eat properly and enough rest not to be tired on your test day. If you have done the correct studying procedures prior to 48 hours of your test day and you just recap and rest you should do really well on your exam.