## Precalculus (6th Edition) Blitzer

The number of ways to select the two favorite jokes out of 6 jokes is $15$ .
We know that: ${}_{n}{{C}_{r}}=\frac{n!}{r!\left( n-r \right)!}$ So, from the provided information, \begin{align} & n=6 \\ & r=2 \\ \end{align} Then, we have to find the number of combinations of 6 things taken 2 at a time: \begin{align} & {}_{6}{{C}_{2}}=\frac{6!}{2!\left( 6-2 \right)!} \\ & =\frac{6!}{2!4!} \\ & =\frac{6\times 5\times 4!}{2!4!} \\ & =15 \end{align} Thus, the number of ways of selecting the two favorite jokes out of 6 jokes is $15$.