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Indian Mathematical Olympiad 1986 - Problem 8

Source:

August 13, 2009
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Problem Statement

Suppose A1,,A6 A_1,\dots, A_6 are six sets each with four elements and B1,,Bn B_1,\dots,B_n are n n sets each with two elements, Let S \equal{} A_1 \cup A_2 \cup \cdots \cup A_6 \equal{} B_1 \cup \cdots \cup B_n. Given that each elements of S S belogs to exactly four of the A A's and to exactly three of the B B's, find n n.