## Thinking Mathematically (6th Edition)

The number of possible combinations if r items are taken from n items is nCr =$\frac{n!}{r!(n-r)!}$ The number of ways that 3 jokes can be ranked is = 6C3 x 1! =$\frac{6!}{(6-3)!3!}$ =$\frac{6*5*4*3!}{3!3!}$ =$\frac{6*5*4}{3*2*1}$ = 20 ways