Problem #WSP-000137

Problems Methods Pigeonhole principle Pigeonhole principle (finite number of poits, lines etc.)

Problem

Margaret and Angelina decided to move to the second dimension. Now Margaret marked five points with both integer coordinates on a plane with red crayon. While Angelina marked a midpoint for every pair of red points with blue crayon. Prove that at least 1 of the blue points has both integer coordinates.