olymmath

VMO 2011

Vietnam Mathematical Olympiad 2011.

Other problems

Problem 4

A convex pentagon ABCDEABCDE satisfies that the sidelengths and AC,AD≤3.AC,AD\leq \sqrt 3. Let us choose 20112011 distinct points inside this pentagon. Prove that there exists an unit circle with centre on one edge of the pentagon, and which contains at least 403403 points out of the 20112011 given points. {Edited} {I posted it correctly before but because of a little confusion deleted the sidelength part, sorry.}