## Precalculus (10th Edition)

$1$
We know that $C(n,r)=\dfrac{n!}{(n-r)!r!}$, $0!=1$, and $C(n,0)=1$. Hence, $C(15,15)=\dfrac{15!}{(15-15)!\cdot15!}=\dfrac{15!}{0!\cdot15!}=1$