Divided into 100 congruent equilateral triangles
Source: Baltic Way 1993
June 15, 2012
combinatorics proposedcombinatorics
Problem Statement
An equilateral triangle is divided into congruent equilateral triangles. What is the greatest number of vertices of small triangles that can be chosen so that no two of them lie on a line that is parallel to any of the sides of the triangle ?