Answer
$_{12}P_4=11,880$
Work Step by Step
$_nP_r=\frac{n!}{(n-r)!}$
$n=12$ and $r=4$
$_{12}P_4=\frac{12!}{(12-4)!}=\frac{12!}{8!}$.
But, $12!=12\times11\times10\times9\times(8\times7\times6\times\times4\times3\times2\times1)=12\times11\times10\times9\times8!$
$_{12}P_4=\frac{12\times11\times10\times9\times8!}{8!}=12\times11\times10\times9=11,880$
