## Thinking Mathematically (6th Edition)

The number of possible permutations if r items are taken from n items is nPr = $\frac{n!}{(n-r)!}$ 9P4 = $\frac{9!}{(9-4)!}$ = $\frac{9*8*7*6*5!}{5!}$ Since 5! is in both the numerator and the denominator, cancel 5! in the numerator and the denominator. 9*8*7*6 = 3024