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12 men and 12 women at the dance

Source: XI May Olympiad (Olimpiada de Mayo) 2005 L2 P4

September 19, 2022
combinatorics

Problem Statement

At a dance there are 1212 men, numbered 11 to 1212, and 1212 women numbered 11 to 1212. Each man is assigned a “secret friend” among the 1111 others. They all danced all the pieces. In the first piece each man danced with the woman who has the same number. From then on, each man danced the new piece with the woman who had danced the piece earlier with his secret friend. In the third piece the couples were: https://cdn.artofproblemsolving.com/attachments/c/d/f5ea0931e5751739c1ba556f84ab5736f2d11a.png Find the number of each man's secret friend.