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'Weekly Problem 31 - 2006' printed from http://nrich.maths.org/
Take one blue unit cube and glue six further blue unit cubes to each of its faces (to make a 3D cross).
If unit cubes coloured yellow are now glued face-to-face to all the spare faces of the blue cross, how many yellow unit cubes are required?
This problem is taken from the UKMT Mathematical Challenges.View the previous week's solution