Chapter 12 - Data Analysis and Probability - 12-6 Permutations and Combinations - Practice and Problem-Solving Exercises - Page 754: 35

10

Use the formula of combination: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$. Plug in 10 for N and 9 for R: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$ $_{10}$C$_{9}$=$\frac{10!}{9!(10-9)!}$ -simplify like terms- $_{10}$C$_{9}$=$\frac{10!}{9! (1!)}$ -write using factorial- $_{10}$C$_{9}$=$\frac{10*9*8*7*6*5*4*3*2*1}{(9*8*7*6*5*4*3*2*1)(1)}$ -simplify- $_{10}$C$_{9}$=10