21 tiles, some white and some black, in a 3 x 7 rectangle
Source: OLCOMA Costa Rica National Olympiad, Final Round, 2016 Shortlist LR1 day1 (logical reasoning)
September 22, 2021
combinatoricstilesrectangle
Problem Statement
With tiles, some white and some black, a rectangle is formed. Show that there are always four tokens of the same color located at the vertices of a rectangle.