Question

If $n_{P-4}=360$, find the value of n.

Answer 1

We have,
$n_{P-4}=360$
$\Rightarrow \frac{n!}{(n-4)!}=360$
$\Rightarrow \frac{n(n-1)(n-2)(n-3)(n-4)!=360}{(n-4)!}$
$\Rightarrow n(n-1)(n-2)(n-3)=6\times 5\times 4\times 3$
Hence, n=6 [13y comparing]