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2008 PUMaC Combinatorics A7

Source:

October 4, 2019
combinatorics

Problem Statement

Joe makes two cubes of sidelengths 99 and 1010 from 17291729 randomly oriented and randomly arranged unit cubes, which are initially unpainted. These cubes are dipped into white paint. Then two cubes of sidelengths 11 and 1212 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 99 and 1010 into paint and cubes of sides 11 and 1212 into paint remover ad nauseam. What is the limit of the expected number of painted unit cube faces immediately after dipping in paint remover?