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MathNet 2008-part-01 — 165 problems (EN–VI) Question 60

Math Olympiad Vault · MathNet 2008-part-01 — 165 problems (EN–VI)

Question 60

In a school class with $3n$ children, any two children make a common present to exactly one other child. Prove that for all odd $n$ it is possible that the following holds:
For any three children $A$, $B$ and $C$ in the class, if $A$ and $B$ make a present to $C$ then $A$ and $C$ make a present to $B$.