Answer
40
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
