Hi guzzlers,

Wednesday is Pi Day, an annual date of celebration in the mathematical community because March 14, or 3/14, using the US convention for dates, looks like 3.14, which is pi to two decimal places.

Pi – usually written as the Greek letter π – is the ‘circle constant’. Take any circle you like. Whatever the size, the ratio of its circumference to its diameter is pi. If you want to know more about this numerical marvel, please scroll down. But first, today’s three puzzles.

1. Move one matchstick below to make the equation **approximately** correct:

2. G**odd**frey and St**even** are **p****i**-ous ninth-century monks. It is the summer of 888 AD, and they have agreed they will share the job of writing the town records every day. Goddfrey does every day that contains an ODD digit in the date. Steven does all other days. They begin

- 20.08.888 Steven
- 21.08.888 Goddfrey
- 22.08.888 Steven
- 23.08.888 Goddfrey
- 24.08.888 Steven
- 25.08.888 Goddfrey
- 26.08.888 Steven
- 27.08.888 Goddfrey
- 28.08.888 Steven

*When is the next day when Steven has to work?*

3. I bought a delicious pie the other day. It cost somewhere between £1.50 and £2.75 inclusive. I gave a 24 per cent tip, and the total price was still an exact number of pence. When I paid with a £5 note I received five coins in my change (the fewest I could have been given).

*How much did the pie cost?** And what has this question got to do with pi?*

[For non-Brits, coins in circulation have values of 1p, 2p, 5p, 10p, 20p, 50p, £1 and £2]

Today’s puzzles come from Chris Smith, surely the most ins-**pi**-rational maths teacher in the UK. Watch his hilarious song about pi that he performed with his students at Grange Academy, Kilmarnock.

Chris is also well known in the maths community for his brilliant weekly newsletter for maths teachers. It has been going for more than a decade, and has 2,500 subscribers from around the world. Email him if you want to be added to his list. (Of course his email address has **pi **in it!) Or follow him on Twitter.

Now let’s circle back to pi. Here’s a bluffer’s guide, here is an interview with the Japanese man who memorised more than 100,000 digits of pi, here’s a piece on the pi poem, or piem, here’s an article about the Welshman who was the first to use pi, and here is an investigation about rivers and pi. If you don’t want to read anything, here is a gallery of images of pi.

I’ll be back at 5pm GMT with the solutions. And please, NO SPOILERS!

Instead, chat about your favourite thing about pi.

*I set a puzzle here every two weeks on a Monday.** **I’m always on the look-out for great puzzles. If you would like to suggest one, email me.*

*I’m the author of several books of popular maths, including the puzzle books Can You Solve My Problems? and Puzzle Ninja.*