## Articles

**Burkard Polster**and

**Marty Ross'**method for working out the day on which someone was born from their birthday really fast.

*x*

^{k}? If you're up to speed with your calculus, you can probably rattle the answer off by heart. But can you prove it?

**Chris Sangwin**introduces an ingenious method for deriving the integral from first principles.

*x*

^{k}really the best one?

**Chris Sangwin**makes an interesting case that it is not.

**Burkard Polster**and

**Marty Ross**explain why, and explore the maths behind bell ringing.

**Nicholas Mee**discovers, that would be far too simple. In fact, the length of a day varies throughout the year. If you plot the position of the Sun in the sky at the same time every day, you get a strange figure of eight which has provided one artist with a source for inspiration.

**Liz Newton**takes you on a journey of origami, maths and science.