SAT Math

Answer: E - 660 delegations can be formed. We choose 2 boys from the group of 12 boys. These are combinations, where r = 2 and n = 12.
12!/2!(12-2)! = 12!/2!10! = (12×11)/2 = 6×11 = 66

Then we choose 1 girl from the group of 10 girls. These are combinations, where
r = 1 and n = 10.
10!/1!(10-1)! = 10!/9! = 10

For every combination of boys, we have 10 combinations of girls. Therefore, the total number of delegations of 2 boys and 1 girl is 66 × 10 = 660.