An example can be helpful: Given Set A = {1, 2, 3} This is the power Set of A P(A) = {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}} (All the subsets

An example can be helpful: Given Set A = {1, 2, 3} This is the power Set of A P(A) = {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}} (All the subsets of A including the empty set and A itself) 3 choose 2 = 3 (If you look in the power set, you'll see that there are only 3 ways to choose 2 items out of 3) Note that order does not matter.