#### Answer

$100$

#### Work Step by Step

RECALL:
$P(n, r) = \dfrac{n!}{(n-r)!}$
Use the formula above to obtain:
$P(100, 1) = \dfrac{100!}{(100-1)!}
\\P(100, 1) = \dfrac{100!}{99!}
\\P(100, 1) = \dfrac{100(99!)}{99!}$
Cancel the common factor $99!$ to obtain:
$P(100, 1) = 100$