MathDB
Betting money on sum of areas

Source: Sharygin geometry olympiad 2016, grade 10, Final Round, Problem 4.

August 5, 2016
combinatoricsgeometryareagamegame strategy

Problem Statement

The Devil and the Man play a game. Initially, the Man pays some cash ss to the Devil. Then he lists some 9797 triples {i,j,k}\{i,j,k\} consisting of positive integers not exceeding 100100. After that, the Devil draws some convex polygon A1A2...A100A_1A_2...A_{100} with area 100100 and pays to the Man, the sum of areas of all triangles AiAjAkA_iA_jA_k. Determine the maximal value of ss which guarantees that the Man receives at least as much cash as he paid.
Proposed by Nikolai Beluhov, Bulgaria