MathDB
Junior Combinatorics

Source: 2015 JBMO TST - Macedonia, Problem 5

December 31, 2015
polygonColoringcombinatorics2015

Problem Statement

AA and BB are two identical convex polygons, each with an area of 20152015. The polygon AA is divided into polygons A1,A2,...,A2015A_1, A_2,...,A_{2015}, while BB is divided into polygons B1,B2,...,B2015B_1, B_2,...,B_{2015}. Each of these smaller polygons has a positive area. Furthermore, A1,A2,...,A2015A_1, A_2,...,A_{2015} and B1,B2,...,B2015B_1, B_2,...,B_{2015} are colored in 20152015 distinct colors, such that AiA_i and AjA_j are differently colored for every distinct ii and jj and BiB_i and BjB_j are also differently colored for every distinct ii and jj. After AA and BB overlap, we calculate the sum of the areas with the same colors. Prove that we can color the polygons such that this sum is at least 11.