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 with side length . It is divided into identical small equilateral triangles with side length . On every vertex of the triangles there is a number. In a move we can choose a rhombus and add or subtract from all numbers on the vertices of the rhombus. Let point have coordinates where is the number of the row and is the position on it from left to right. On the vertices there are 's and on the other vertices there are 's. Is it possible, after some operations, all the numbers to become equal?