Probably a simple maths question

There was apparently a question on University Challenge last night, and I can't work out how to work it out. The question is this: if you have a pool of 7 people, how many possible 4-person teams could you make from it? I know the answer, but I don't know the method of calculating it. I could do it using pen and paper, but not in anything like the time allowed to answer it on a quiz show, so there's clearly some trick to this sort of problem.



Assume, of course, that a team using persons 1/2/3/4 is the same as 4/3/2/1.



Any ideas?

via JREF Forum http://forums.randi.org/showthread.php?t=263040&goto=newpost