MathDB
rectangles in the coordinate plane

Source: Japan Mathematical Olympiad Finals, Problem 5

February 7, 2010
geometryrectangleanalytic geometrycombinatorics proposedcombinatorics

Problem Statement

Let S S be a set of 2002 points in the coordinate plane, no two of which have the same x\minus{} or y\minus{}coordinate. For any two points P,QS P,Q \in S, consider the rectangle with one diagonal PQ PQ and the sides parallel to the axes. Denote by WPQ W_{PQ} the number of points of S S lying in the interior of this rectangle. Determine the maximum N N such that, no matter how the points of S S are distributed, there always exist points P,Q P,Q in S S with WPQN W_{PQ}\ge N.