Combinatorics from "The editors"
Source: Romania 2017 IMO TST 1, problem 2
March 18, 2018
combinatorics
Problem Statement
Consider a finite collection of 3-element sets , no two of which share more than one element, whose union has cardinality 2017. Show that the elements of this union can be coloured with two colors, blue and red, so that at least 64 elements are blue and each has at least one red element.