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MathNet 2011 Question 35

Math Olympiad Vault · MathNet 2011

Question 35

Consider $n$ persons, each of them speaking at most 3 languages. From any 3 persons there are at least two which speak a common language.

i) For $n \le 8$, exhibit an example in which no language is spoken by more than two persons.

ii) For $n \ge 9$, prove that there exists a language which is spoken by at least three persons.