If There's a Loser, Everyone Else is Popular

In a class of 2015 2015 kids, any set of 3 3 kids contains at least one pair of friends. It turns out that in any possible arrangement, the most popular kid will have at least k k friends. Find k k .

Details and Assumptions

  • Friendship is a mutual relation.
  • The most popular kid is the kid with the most friends.
  • If two people tie for most number of friends, then randomly select one of them to be the most popular.
  • This problem is not original.


The answer is 1007.

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1 solution

Nathan Ramesh
Dec 5, 2014

The answer is 1007 1007 . Suppose the most popular kid has only 1006 1006 friends (or less). Then everyone but the most popular kid and his friends must be friends, so these people each have 1007 1007 friends, contradiction.

Nice one! Upvoted!

Pranjal Jain - 6 years, 6 months ago

We still need to show that it is possible for the most popular kid to have 1007 friends. One possible configuration is if there are 2 groups, with sizes 1006 and 1007. Everyone in each group is friends with each other, and no one is friends with anyone from the other group.

Joe Mansley - 1 year, 11 months ago

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