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Problem 6 (2021 AIME II)

AIMEHard

From module Inclusion-Exclusion

Problem

For any finite set SS, let S|S| denote the number of elements in SS. Find the number of ordered pairs (A,B)(A, B) such that AA and BB are (not necessarily distinct) subsets of {1,2,3,4,5}\{1, 2, 3, 4, 5\} that satisfy AB=ABAB|A| \cdot |B| = |A \cap B| \cdot |A \cup B|

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