2008 PUMaC Combinatorics A7
Source:
October 4, 2019
combinatorics
Problem Statement
Joe makes two cubes of sidelengths and from randomly oriented and randomly arranged unit cubes, which are initially unpainted. These cubes are dipped into white paint. Then two cubes of sidelengths and are formed from the same unit cubes, again randomly oriented and randomly arranged, and these cubes are dipped into paint remover. Joe continues to alternately dip cubes of sides and into paint and cubes of sides and into paint remover ad nauseam.
What is the limit of the expected number of painted unit cube faces immediately after dipping in paint remover?