Question

A librarian chooses seven holiday books from a selection of ten to be displayed in the window of the library. In how many different ways can she choose the group of seven books?

Answer 1

She is choosing an unordered subset of 7 from 10, so the number of ways is C(10,7) = 10!/(7!3!) = (10·9·8)/(3·2·1) = 120.