Unless you count looking over my notes in the first 5 minutes of class before the pass out the exams, I don't study. Although I skimmed through the wikipedia articles on the Mexican-American War and the Civil War last night. I probably failed the (History) exam, but I'm sure I passed the class.
I still average B's on most of my other classes though, even with my minimal studying practices.
Physics, probably about 5 hours
Math, maybe 3 hours
Ochem, about 20 or so should do it.
American Indian studies, I will look at one of the books 5 minutes before the test gets handed out maybe.