# Chapter 12 - Data Analysis and Probability - Chapter Review - Page 789: 31

20

#### Work Step by Step

Use the formula of combination: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$. Plug in 6 for N and 3 for R: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$ $_{6}$C$_{3}$=$\frac{6!}{3!(6-3)!}$ -simplify like terms- $_{6}$C$_{3}$=$\frac{6!}{3! (3!)}$ -write using factorial- $_{6}$C$_{3}$=$\frac{6*5*4*3*2*1}{(3*2*1)(3*2*1)}$ -simplify- $_{6}$C$_{3}$=20

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