Originally Posted by

**Jose27** For 1) you have to find all subsets of A that don't contain 1 and 2 simultaneously : Subsets of 1 element you have all 4, of two elements you could have 6, but of those one is {1,2} so you can only have 5, of three elements you could have 4 but two are {1,2,3} and {1,2,4} so you can only have 2, and finally you can't have the whole set since it contains 1 and 2. So now just list these subsets: there are 12 (including the empty set)

For 2) the reasoning is analogous, only now you have to find the subsets that have 1 and 2