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In three sets Q, R, and S, the following conditions are found: in Q intersect R. there are 9 elements in Q intersect S, there are 4 elements in R intersect S, there are 11 elements if (Q Intersect R) union (Q Intersect S) union (R intersect S) includes 18 elements, how many elements are in Q intersect R intersect S?
Answered by oobleck
9+4+11-18 = 6