Combinatorics
Source: Baltic Way 2015
November 8, 2015
combinatorics
Problem Statement
There are members in a ladies' club.Each lady has had tea (in private) with exactly of her lady friends.The Board,consisting of the most distinguished ladies,have all had tea with one another.Prove that the entire club may be split into two groups in such a way that,with in each group,any lady has had tea with any other.