Geometry: Common Core (15th Edition)

a) We use the permutation equation: We know that: $_nP_r = \frac{n!}{(n-r)!}$ $_{12}P_3 = \frac{12!}{(12-3)!}$ $\frac{12!}{9!}$ We also know that: $x! = x(x-1)(x-2)...(1)$ Thus, we have: 1320 b) We know that: $_nP_r = \frac{n!}{(n-r)!}$ $_{12}P_5 = \frac{12!}{(12-5)!}$ $\frac{12!}{7!}$ We also know that: $x! = x(x-1)(x-2)...(1)$ Thus, we have: 95,040