4) in how many different ways can four people be put into three subsets containing two people, one person, and one person?

Assuming order doesn't matter:

From the total 4 people, you choose 2 - this is .

From the remaining 2 people, you choose 1 - this is .

From the last person, you choose that person - this is

So there are 6*2*1 = 12 possible ways.

Note: is the binomial coefficient

noncoplanar points are points that do not lie on the same line.