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Can you explain why every year must contain at least one Friday the thirteenth?
What is the greatest number of Friday the thirteenths that can fall in one year?
Imagine you are suspending a cube from one vertex and allowing it to hang freely. What shape does the surface of the water make around the cube?
Given the nets of 4 cubes with the faces coloured in 4 colours, build a tower so that on each vertical wall no colour is repeated, that is all 4 colours appear.