How many ways can a person select 3 videotapes from a collection of 10 tapes?

If the 10 videotapes are distinct (different) and the order of selection is immaterial, then there are

C (10,3) = 10! / (3! (10-3) !) = 10! / (3!7!) = 10*9*8 / (1*2*3) = 120

ways to select three videotapes out of 10.