Problem

Source: 42nd International Tournament of Towns, Junior A-Level P3, Fall 2020

Tags: game, combinatorics, Tournament of Towns



Alice and Bob are playing the following game. Each turn Alice suggests an integer and Bob writes down either that number or the sum of that number with all previously written numbers. Is it always possible for Alice to ensure that at some moment among the written numbers there are at least a hundred copies of number 5? at least a hundred copies of number 10? Andrey Arzhantsev