Ok, so I had to take a math exam in real life, and dreamt about it just the night before:
First of all, I missed the train and almost came in late. When I arrived, I met a former classmate of mine (who doesn't even study), and in total, we were like 6 people taking the exam. Also, for some reason, it started 13:00 in my dream (as opposed to 12:00). It was 14:40 then (in case you wonder, I had a look at my watch in the dream), I was just halfway through the thing, and the prof went: "Okay, so this is supposed to take 3 hours, but we'll just stop now." My former classmate got super pissed off, and stormed out of the room. I was pretty angry too, because it was an important exam and I could only get half the points at best. Then the prof continued: "... also, we're not going to count this as an exam, but instead - remember that training unit we did some time ago?" Then she went over to me, said: "Well, you should have explained it in more detail", and handed me a sheet of paper, on which I appearently had written down ONE SINGLE FORMULA.
Then I couldn't take it anymore and woke up. At 5:28 am. After 3 hours of sleep.
By the way, reading mine and some of the other dreams here, I think it's incredible how you can dream stuff like that. You'd expect yourself to go "Nope, can't be real!" during your dream, and then... well, who knows what would happen.