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Intersection + Union

Source: AMC 10 2008A Problem 23

February 22, 2008
AMC

Problem Statement

Two subsets of the set S\equal{}\{a,b,c,d,e\} are to be chosen so that their union is S S and their intersection contains exactly two elements. In how many ways can this be done, assuming that the order in which the subsets are chosen does not matter? <spanclass=latexbold>(A)</span> 20<spanclass=latexbold>(B)</span> 40<spanclass=latexbold>(C)</span> 60<spanclass=latexbold>(D)</span> 160<spanclass=latexbold>(E)</span> 320 <span class='latex-bold'>(A)</span>\ 20 \qquad <span class='latex-bold'>(B)</span>\ 40 \qquad <span class='latex-bold'>(C)</span>\ 60 \qquad <span class='latex-bold'>(D)</span>\ 160 \qquad <span class='latex-bold'>(E)</span>\ 320