How many distinct proper subsets are there of the set N={5,50,70,20}

Question

How many distinct proper subsets are there of the set N={5,50,70,20}

Answer 1

4 elements, so there are 2^4 subsets = 16 subsets. But PROPER subsets means subtract 1, as the set of all 4 elements is an improper subset. 16-1 = 15 proper subsets. That also includes the null set.

There is

one null set which has no elements, designated as a zero with a slash through it

4 subsets with just one element each, {5},{50}, {70} and {20}

6 subsets with two elements each {5,50}, {5,70}, {5,20}, {50,70},{50,20} {70,20}

4 subsets with three elements each, each one will be missing one of the 4 elements

1 subset (improper) with 4 elements= set N

sum them, except for the last, and you get 1+4+6+4 = 15 proper subsets