## Precalculus (6th Edition) Blitzer

The number of ways to select the three favorite jokes out of the 6 jokes is $20$.
We know that: ${}_{n}{{C}_{r}}=\frac{n!}{r!\left( n-r \right)!}$ So, from the provided information, \begin{align} & n=6 \\ & r=3 \end{align} Then, we have to find the number of combinations of 6 things take 3 at a time: \begin{align} & {}_{6}{{C}_{3}}=\frac{6!}{3!\left( 6-3 \right)!} \\ & =\frac{6!}{3!3!} \\ & =\frac{6\times 5\times 4\times 3!}{3!3!} \\ & =20 \end{align} Thus, the number of ways to select the three favorite jokes out of the 6 jokes is $20$.