Answer
The answer is below
Work Step by Step
We can prove this easily with math. We know that n = r.
We know that:
$_nC_r =\frac{_nP_r}{r!} = \frac{n!}{(n-r)!r!}$
So it follows:
$_nC_n =\frac{_nP_n}{n!} = \frac{n!}{(n-n)!n!}$
$ \frac{n!}{0!n!}$
Since 0! = 1:
$\frac{n!}{n!}$ = 1
