MathDB
JBMO Shortlist 2021 C3

Source: JBMO Shortlist 2021

July 2, 2022
JuniorBalkanshorlist2021combinatoricsProcess

Problem Statement

We have a set of 343343 closed jars, each containing blue, yellow and red marbles with the number of marbles from each color being at least 11 and at most 77. No two jars have exactly the same contents. Initially all jars are with the caps up. To flip a jar will mean to change its position from cap-up to cap-down or vice versa. It is allowed to choose a triple of positive integers (b;y;r){1;2;...;7}3(b; y; r) \in \{1; 2; ...; 7\}^3 and flip all the jars whose number of blue, yellow and red marbles differ by not more than 11 from b,y,rb, y, r, respectively. After nn moves all the jars turned out to be with the caps down. Find the number of all possible values of nn, if n2021n \le 2021.