## Geometry: Common Core (15th Edition)

Order does not matter, so we use the equation for combinations. We know that: $_nC_r =\frac{_nP_r}{r!} = \frac{n!}{(n-r)!r!}$ $_{24}C_6 = \frac{24!}{(24-6)!6!}$ We also know that: $x! = x(x-1)(x-2)...(1)$ Thus, we have: 128,478