Answer
220 different 9-person juries
Work Step by Step
Use the formula of combination: $_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$. Plug in 12 for N and 9 for R because we have to find the combination of 12 jurors chosen 9 at a time:
$_{n}$C$_{r}$=$\frac{n!}{r!(n-r)!}$
$_{12}$C$_{9}$=$\frac{12!}{12!(12-9)!}$ -simplify like terms-
$_{12}$C$_{9}$=$\frac{12!}{9! (3!)}$ -write using factorial-
$_{12}$C$_{9}$=$\frac{12*11*10*9*8*7*6*5*4*3*2*1}{(9*8*7*6*5*4*3*2*1)(3*2*1)}$ -simplify-
$_{12}$C$_{9}$=220
There are 220 different 9-person juries
