MathDB
Combinatorics

Source: Baltic Way 2015

November 8, 2015
combinatorics

Problem Statement

There are 100100 members in a ladies' club.Each lady has had tea (in private) with exactly 5656 of her lady friends.The Board,consisting of the 5050 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.