A circle is inscribed in an equilateral triangle. Smaller circles touch it and the sides of the triangle, the process continuing indefinitely. What is the sum of the areas of all the circles?

Can you work through these direct proofs, using our interactive proof sorters?

Watch the video to see how to add together an arithmetic sequence of numbers efficiently.

What can you deduce about prime numbers in arithmetic progression?

Can you work out what happens when this mad robot sets off?

An arithmetic progression is shifted and shortened, but its sum remains the same...

A short challenge concerning the decay of medicines in the body.