St. Petersburg MO 2017 Grade 9 P7
Source: St. Petersburg MO 2017 Grade 9 P7
May 3, 2018
combinatorics
Problem Statement
Divide the upper right quadrant of the plane into square cells with side length . In this quadrant, cells are colored, show that there’re at least cells (possibly including the colored ones) that at least one of its neighbors are colored.