Answer
$840$
Work Step by Step
Use the formula $P(n,r)=\dfrac{n!}{(n-r)!}$.
Here, $n=7$ and $r=4$ so substitute these values into the formula above to obtain:
$P(7,4)=\dfrac{7!}{(7-4)!}\\\\
P(7,4)=\dfrac{7!}{3!}\\\\
P(7,4)=\dfrac{7{\times}6{\times}5{\times}4{\times}3{\times}2{\times}1}{3{\times}2{\times}1}$
Cancel out common factors to get:
$P(7,4) =7\times6\times5\times4\\
P(7, 4) =840$
