At least four monochromatic triangles...
Source: Finnish Mathematics Competition 2000, Final Round, Problem 4
November 14, 2011
combinatorics unsolvedcombinatorics
Problem Statement
There are seven points on the plane, no three of which are collinear. Every pair of points is connected with a line segment, each of which is either blue or red. Prove that there are at least four monochromatic triangles in the fi gure.