MathDB
Replacing two numbers by average, at most cn moves

Source: 2024 Israel TST Test 2 P3

November 7, 2023
Game Theorycombinatoricsaveragesasymptotics

Problem Statement

Let 0<c<10<c<1 and nn a positive integer. Alice and Bob are playing a game. Bob writes nn integers on the board, not all equal. On a player's turn, they erase two numbers from the board and write their arithmetic mean instead. Alice starts and performs at most cncn moves. After her, Bob makes moves until there are only two numbers left on the board. Alice wins if these two numbers are different, and otherwise, Bob wins. For which values of cc does Alice win for all large enough nn?