MathDB
Operation on a grid of equilateral triangles

Source: Bulgaria JTST 2016 P4 day 1

August 27, 2019
combinatorics proposedcombinatorics

Problem Statement

Given is equilateral triangle ABCABC with side length n3n \geq 3. It is divided into n2n^2 identical small equilateral triangles with side length 11. On every vertex of the triangles there is a number. In a move we can choose a rhombus and add or subtract 11 from all 44 numbers on the vertices of the rhombus. Let point DD have coordinates (3,2)(3,2) where 33 is the number of the row and 22 is the position on it from left to right. On the vertices A,B,C,DA,B,C,D there are 11's and on the other vertices there are 00's. Is it possible, after some operations, all the numbers to become equal?