91 students in a school are distributed in three classes
Source: Norwegian Mathematical Olympiad 1997 - Abel Competition p3b
February 11, 2020
combinatorics
Problem Statement
Ninety-one students in a school are distributed in three classes. Each student took part in a competition. It is known that among any six students of the same sex some two got the same number of points. Show that here are four students of the same sex who are in the same class and who got the same number of points.