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2020 AMC 12B Problems/Problem 15

Revision as of 22:18, 7 February 2020 by Quadraticfunctions (talk | contribs) (→‎Problem)

Problem

There are $10$ people standing equally spaced around a circle. Each person knows exactly $3$ of the other $9$ people: the $2$ people standing next to her or him,as well as the person directly across the circle. How many ways are there for the $10$ people to split up into $5$ pairs so that the members of each pair know each other?

$(A) 11$ $(B) 12$ $(C) 13$ $(D) 14$ $(E) 15$

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