Answer
56 different 3-CDs
Work Step by Step
Use the formula of combination: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$. Plug in 8 for N and 3 for R because we have to find the number of combination of 8CDs chosen 3 at a time:
$_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$
$_{8}$C$_{3}$=$\frac{8!}{3!(8-3)!}$ -simplify like terms-
$_{8}$C$_{3}$=$\frac{8!}{3! (5!)}$ -write using factorial-
$_{8}$C$_{3}$=$\frac{8*7*6*5*4*3*2*1}{(3*2*1)(5*4*3*2*1)}$ -simplify-
$_{8}$C$_{3}$=56
There are 56 different 3-CDs
