## Thinking Mathematically (6th Edition)

$21$
If we want to choose $k$ elements out of $n$ disregarding the order, not allowing repetition, we can do this in $_{n}C_k=\frac{n!}{k!(n-k)!}$ ways. Hence here because we have $7$ spots for $2$ people, $_{7}C_2=\frac{7!}{2!(7-2)!}=7\cdot6/2=21$