Math.skillz

simple! draw a Venn Diagram! Thus, the answer is $52$ people.

Well if he has $12$ shirts, he has $12$ to choose from. So $12$ for the first choice, $11$ for the second choice (because the first has been used), and $10$ for the third choice. Thus, he has $12\cdot11\cdot10$ choices, but they are counted $6$ times each, so the answer is $\boxed{220}$.