MathDB
red and blue balls in an urn , 1024 in total

Source: 2020 Dürer Math Competition Finals Day2 E+7 https://artofproblemsolving.com/community/c1622639_2020_

January 7, 2022
combinatoricsgameColoring

Problem Statement

There are red and blue balls in an urn : 10241024 in total. In one round, we do the following: we draw the balls from the urn two by two. After all balls have been drawn, we put a new ball back into the urn for each pair of drawn balls: the colour of the new ball depends on that of the drawn pair. For two red balls drawn, we put back a red ball. For two blue balls, we put back a blue ball. For a red and a blue ball, we put back a black ball. For a red and a black ball, we put back a red ball. For a blue and a black ball, we put back a blue ball. Finally, for two black balls we put back a black ball. Then the next round begins. After 1010 rounds, a single ball remains in the urn, which is red. What is the maximal number of blue balls that might have been in the urn at the very beginning?