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All in the Mind

Imagine you are suspending a cube from one vertex (corner) and allowing it to hang freely. Now imagine you are lowering it into water until it is exactly half submerged. What shape does the surface of the water make around the cube?

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Qqq..cubed

It is known that the area of the largest equilateral triangular section of a cube is 140sq cm. What is the side length of the cube? The distances between the centres of two adjacent faces of another cube is 8cms. What is the side length of this cube? Another cube has an edge length of 12cm. At each vertex a tetrahedron with three mutually perpendicular edges of length 4cm is sliced away. What is the surface area and volume of the remaining solid?

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Painting Cubes

Imagine you have six different colours of paint. You paint a cube using a different colour for each of the six faces. How many different cubes can be painted using the same set of six colours?

Nine Colours

Stage: 3 and 4 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

We have received a very elegant strategy for solving this problem from Tom and Adam, of Alcester Grammar School in England:

We have found a solution to this puzzle. Our solution works, because we selected all the nine colours for the bottom face. Their position did not matter as long as there was one of each on the base.

For each colour, we then moved up one level, right one space (if they were on the far right already, they moved to the left row), and forward once (if they were at the back already, they moved to the front row).

We repeated the same procedure to fill the top level.

This ensured that there was one of each colour in each row, column, and on each level. Because of this, each of the faces could only contain one of each colour, as when we consider a whole face, all of the colours will just shift one place, inwards, and move off the row and level that they were on before. Also, as every colour was on the initial face, there would have to be every single colour on all the other faces too.

Thank you Tom and Adam for such a neat solution.

Anybody who would like to check that the procedure works can return to the problem page and try the strategy out for themselves.

Chris from Alcester Grammar School sent us his solution:

ccchris' solution

And so did Giancarlo from Haut-Lac School:

Giancarlo's solution