### Building Tetrahedra

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

### 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?

### 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.

# Pencil Turning

##### Stage: 4 Short Challenge Level:

Ans 1:1

Let AB have length 3r. The distance moved by A is then the circumference of a semicircle radius 3r (3$\pi$r). C moves along a circle of radius 2r (2$\pi$r), followed by a semicircle of radius r ($\pi$r). The total distance moved by C is therefore also 3$\pi$r.

This problem is taken from the UKMT Mathematical Challenges.