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Cubic Covering

Age 14 to 16 Short
Challenge Level
We first imagine the cross with the blue cubes only:
 

We now glue the yellow faces to the up and bottom faces of the blue cross. We require 5 yellow cubes for wrapping each of the two blue cubes. (We used transparent yellow cubes)
 
        

Now we need one yellow cube for each of the four corners:
Finally, we have 4 faces to cover, so we need 4 more squares.

Therefore, we used $5+5+4+4 = 18$ yellow cubes.
 

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.
The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
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