Bugs on a chessboard - Switzerland 2011
Source:
March 22, 2011
geometrygeometric transformationcombinatorics proposedcombinatorics
Problem Statement
On each square of an -chessboard, there are two bugs. In a move, each bug moves to a (vertically of horizontally) adjacent square. Bugs from the same square always move to different squares. Determine the maximal number of free squares that can occur after one move.(Swiss Mathematical Olympiad 2011, Final round, problem 10)