## Thinking Mathematically (6th Edition)

The number of possible permutations if r items are taken from n items is nPr = $\frac{n!}{(n-r)!}$ 9P9= $\frac{9!}{(9-9)!}$ = $\frac{9!}{0!}$ = $\frac{362880}{1}$ = 362880 We put 1 on the bottom since 0!=1.