MathDB
painting houses on a nxn board

Source: Lusophon 2012 CPLP P2

August 29, 2018
combinatoricsboard

Problem Statement

Maria has a board of size n×nn \times n, initially with all the houses painted white. Maria decides to paint black some houses on the board, forming a mosaic, as shown in the figure below, as follows: she paints black all the houses from the edge of the board, and then leaves white the houses that have not yet been painted. Then she paints the houses on the edge of the next remaining board again black, and so on. a) Determine a value of nn so that the number of black houses equals 200200. b) Determine the smallest value of nn so that the number of black houses is greater than 20122012.