How many people are at the meeting?
Source: IMO Shortlist 1995, N5
August 10, 2008
combinatoricsgraph theoryExtremal combinatoricsIMO Shortlist
Problem Statement
At a meeting of people, each person exchanges greetings with exactly 3k\plus{}6 others. For any two people, the number who exchange greetings with both is the same. How many people are at the meeting?