Question

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

Answer 1

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.