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Set Theoryhard
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Let U={1,2,3,…,20}U = \{1, 2, 3, \dots, 20\}U={1,2,3,…,20}. Consider two subsets of the Cartesian product U×UU \times UU×U: S1={(x,y)∈U×U:x divides y}S_1 = \{ (x, y) \in U \times U : x \text{ divides } y \}S1​={(x,y)∈U×U:x divides y} S2={(x,y)∈U×U:y divides x}S_2 = \{ (x, y) \in U \times U : y \text{ divides } x \}S2​={(x,y)∈U×U:y divides x} Determine the cardinality of S1∩S2S_1 \cap S_2S1​∩S2​.