Answer
$r!$
Work Step by Step
Comparing
${}_{n}P_{r}=\displaystyle \frac{n!}{(n-r)!}\quad$ and $\quad {}_{n}C_{r}=\displaystyle \frac{n!}{(n-r)!r!}$,
the extra factor in the denominator of ${}_{n}C_{r}$ is $r!$
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