Cutting up an equilateral triangle
Source: All-Russian MO 1999
December 31, 2012
complementary countingcombinatorics unsolvedcombinatorics
Problem Statement
An equilateral triangle of side is divided into equilateral triangles of side . Find the greatest possible number of unit segments with endpoints at vertices of the small triangles that can be chosen so that no three of them are sides of a single triangle.