Stage: 5 Challenge Level: 
The edges in these 4 graphs show the colour pairings of opposite faces of the cubes.
To solve the problem combine all 4 graphs then look for 2 subgraphs, one representing the colours on the front and back walls of the tower and the other representing the colours on the left and right hand walls of the tower, such that each contains all 4 colours and precisely one edge of each numbered cube.
Stage 5 - Reviewed 2012. epsilons. Interactivities. alphas. Visualising. Mathematical reasoning & proof. Manipulating algebraic expressions/formulae. Combinatorics. Networks/Graph Theory. Working systematically.
Published November 2002,December 2002,March 2009,April 2009.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk