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Building Tetrahedra

Can you make a tetrahedron whose faces all have the same perimeter?

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Ladder and Cube

A 1 metre cube has one face on the ground and one face against a wall. A 4 metre ladder leans against the wall and just touches the cube. How high is the top of the ladder above the ground?

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Areas and Ratios

What is the area of the quadrilateral APOQ? Working on the building blocks will give you some insights that may help you to work it out.

Supercomputer

Stage: 4 Short Challenge Level: Challenge Level:2 Challenge Level:2

If $n$ is a positive integer then the units digit of $66^{n}$ is $6$. So when a power of $66$ is divided by $2$, the units digit of the quotient is either $3$ or $8$. Now $66^{66}$ is clearly a multiple of $4$, so $\frac{1}{2}\left(66^{66}\right)$ is even and therefore has units digit $8$ rather than $3$.

This problem is taken from the UKMT Mathematical Challenges.