Question 1186668
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You need to choose 2 of the 4 elements; the number of ways you can do that is "4 choose 2" = C(4,2) = 6.<br>
You can make the list; it should have 6 different subsets.<br>
To make sure you don't count any subset twice, make sure each subset you write has the smaller of the two elements first -- that is, for example, you don't want to have two different subsets {2,4} and {4,2}, because those are the same.<br>
Or of course you could make sure that in each subset you list the larger of the two numbers is first....<br>