Answer
$1680$
Work Step by Step
We know that $P(n,r)=\dfrac{n!}{(n-r)!}.$
Hence,
$P(8,4)=\dfrac{8!}{(8-4)!}=\dfrac{8\cdot7\cdot6\cdot5\cdot4!}{4!}=8\cdot7\cdot6\cdot5=1680$
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