Beckyb Posted April 28, 2016 Share Posted April 28, 2016 How many two-element subsets of (1,2,3,4) are there that do not contain the pair of elements 2 and 4? a) 1 b)2 c)4 d)5 e)6 How did you solve? Explanation please! :) Quote Link to comment Share on other sites More sharing options...
YaSvoboden Posted April 28, 2016 Share Posted April 28, 2016 You can do this by taking 4C2 - 1. Or, this is a pretty easy problem to just go through the combinations. Given the choices, you have at most 6 combinations to identify. Here are the combos: 1,2 1,3 1,4 2,3 2,4 3,4 Look six combinations, but don't count (2,4). So 5 different subsets. Quote Link to comment Share on other sites More sharing options...
Beckyb Posted April 29, 2016 Author Share Posted April 29, 2016 Thanks!:):) You can do this by taking 4C2 - 1. Or, this is a pretty easy problem to just go through the combinations. Given the choices, you have at most 6 combinations to identify. Here are the combos: 1,2 1,3 1,4 2,3 2,4 3,4 Look six combinations, but don't count (2,4). So 5 different subsets. Quote Link to comment Share on other sites More sharing options...
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