MathDB
Problem 4

Source: Paraguayan Mathematical Olympiad 2013

July 25, 2015
combinatorics

Problem Statement

Pedro and Juan are playing the following game: - There are 22 piles of rocks, with XX rocks in one pile and YY rocks in the other pile (X<12,Y<11X < 12, Y < 11). - Each player can draw: -- 11 rock from one of the piles, or -- 22 rocks from one of the piles, or -- 11 rock from each pile, or -- 22 rock from one pile and 11 from the other pile. Each player must perform one of these four operations in their turns. The looser is the one who takes the last rock. Pedro plays first and has a winning strategy. What are the three maximum possible values of (X+YX+Y)?