So if you are trying to find the permutations of a, b, and c, they would be abc, acb, bca, bac, cba, and cab. The combinations would be just abc because order does not matter. The combinations of choosing 2 elements out of a b and c would be ab, cb, and ac.

In summary, the union of 2 sets (AUB) is the set of all outcomes in A or B or both, the intersection is the set of all outcomes in both A and B, and the empty set is the set with no outcomes. 2 events are disjoint if there intersection is the empty set.