MathDB
Kosa and Kechel plays a game with baklavas

Source: Azerbaijan NMO 2023. Junior P5

August 24, 2023
combinatoricsAZE JUNIOR NATIONAL MO

Problem Statement

Baklavas with nuts are laid out on the table in a row at the Nowruz celebration. Kosa and Kechel saw this and decided to play a game. Kosa eats one baklava from either the beginning or the end of the row in each move. Kechel either doesn't touch anything in each move or chooses the baklava he wants and just eats the nut on it. They agree that the first Kosa will start the game and make 2020 moves in each step, and the Kechel will only make 11 move in each step. If the last baklava eaten by the Kosa is a nut, he wins the game. It is given that the number of baklavas is a multiple of 20.20. A)A) If the number of baklavas is 400,400, prove that Kosa will win the game regardless of which strategy Kechel chooses. B)B) Is it always true that no matter how many baklavas there are and what strategy Kechel chooses, Kosa will always win the game?