To solve these questions, we need to use combinations, as the order of selection does not matter. We will calculate the total number of five-person committees, then calculate the number of all-male and all-female committees separately. Finally, we will use these results to find the number of mixed-gender committees by subtracting the all-male and all-female committees from the total.
To find the total number of five-person committees that can be formed from 20 people, we use the combination formula:
\[
\binom{n}{r} = \frac{n!}{r!(n-r)!}
\]
where \( n = 20 \) and \( r = 5 \). Thus, the total number of committees is:
\[
\binom{20}{5} = \frac{20!}{5!(20-5)!} = 15504
\]
To find the number of all-male five-person committees, we use the same combination formula with \( n = 12 \) (the number of males) and \( r = 5 \):
\[
\binom{12}{5} = \frac{12!}{5!(12-5)!} = 792
\]
Similarly, to find the number of all-female five-person committees, we use the combination formula with \( n = 8 \) (the number of females) and \( r = 5 \):
\[
\binom{8}{5} = \frac{8!}{5!(8-5)!} = 56
\]
To find the number of mixed-gender five-person committees, we subtract the number of all-male and all-female committees from the total number of committees:
\[
\text{Mixed-gender committees} = 15504 - 792 - 56 = 14656
\]
- Total number of five-person committees: \(\boxed{15504}\)
- All-male five-person committees: \(\boxed{792}\)
- All-female five-person committees: \(\boxed{56}\)
- Mixed-gender five-person committees: \(\boxed{14656}\)