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2006 Romanian NMO Problems/Grade 9/Problem 4

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Problem

\displaystyle 2n students \displaystyle (n \geq 5) participated at table tennis contest, which took \displaystyle 4 days. Every day, every student played a match. (It is possible that the same pair meets two or more times, in different days). Prove that it is possible that the contest ends like this:

  • there is only one winner;
  • there are \displaystyle 3 students on the second place;
  • no student lost all \displaystyle 4 matches.

How many students won only a single match and how many won exactly \displaystyle 2 matches? (In the above conditions)

Solution

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