Some Identical Items
If at least one item is chosen, the total number of selections that can be made from p items of one kind, q items of another kind, r items of another kind, and so on is (p+1)(q+1)(r+1)... - 1
If at least one item is chosen, the total number of selections that can be made from p items of one kind, q items of another kind, r items of another kind, and so on is (p+1)(q+1)(r+1)... - 1