SOLUTION: Let A = {1, 2, 3, 4, 5, 6, 7}. How many TWO element subsets does A have?

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Question 570704: Let A = {1, 2, 3, 4, 5, 6, 7}. How many TWO element subsets does A have?
Answer by richard1234(5244) About Me  (Show Source):
You can put this solution on YOUR website!
Assume order of the elements doesn't matter, i.e. {3,4} is equivalent to {4,3}.

Then the number of subsets of size 2 is 7C2 = 7*6/2! = 21.