In how many ways can a committee of 12 people, of which 5 must be in the 21−30 age group, 4 must be in the 31−40 age group and 3 must be in the 41−50 age group, be chosen if there are 6 people of each age group?

2 answers

how many possibilities in each subgroup? ... 6Cn

how many ways to combine the different subgroups?
1800. Notice the words be chosen, those are usually in the context of multiplication. Then it's permutations because it's people. (6 permutation 5) * (6 permutation 4) * (6 permutation 3)