TOT 162 1987 Autumn S6 bw equilateral triangles inside equilateral
Source:
April 19, 2020
equilateralsEquilateralColoringcombinatorics
Problem Statement
An equilateral triangle is divided by lines, parallel to its sides, into equilateral triangles, all of the same size. One of the smaller triangles is black while the others are white. It is permitted to intersect simultaneously some small triangles with a line parallel to any side of the original triangle and to change the colour of each intersected small triangle from one colour to the other . Is it always possible to find a sequence of such operations so that the smaller triangles all become white?