## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$48,620$
Recall: $C(n, r)=\dfrac{n!}{(n-r)!r!}$ ways. Thus, \begin{align*} C(18, 9)&=\dfrac{18!}{(18-9)!9!}\\ \\&=\dfrac{18!}{9!9!} \end{align*} Using a calculator gives $C(18, 9)=\dfrac{18!}{9!(18-9)!}=48,620$