[tex]_n{P}_r = \frac{n!}{(n - r)!}[/tex]
[tex]_9P_3 = \frac{9!}{(9 - 3)!}[/tex]
[tex]_9P_3 = \frac{9!}{6!}[/tex]
[tex]_9P_3 = \frac{9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1}{6 * 5 * 4 * 3 * 2* 1}[/tex]
[tex]_9P_3 = 9 * 8 * 7[/tex]
[tex]_9P_3 = 72 * 7[/tex]
[tex]_9P_3 = 504[/tex]
