Maths - Get a piece of the pi

15th March 2013 at 00:00

What it's all about

On Thursday 14 March at 1.59pm, I hosted a free online event to celebrate one of the most enigmatic numbers in maths: pi, writes Marcus du Sautoy.

The number defines the ratio of the circumference of a circle to its diameter. So if a circle is one metre across, then the number of metres it takes to go round the outside of the circle is 3.14159 ... And then the numbers spiral off to infinity in a dizzying dance of digits.

It was these digits that defined the date for our celebration of pi. The first digit gives you the month: 3 for March. The next two, the date: 14. The next digits, the time: 1.59pm.

The event was organised by the new Oxford Connect initiative run by the Department for Continuing Education at the University of Oxford.

The Rhind Papyrus written by the Egyptian scribe Ahmes in about 1650BC approximates pi as 25681 or roughly 3.16. Not bad for a first estimate.

During the hour-long event I introduced some weird and wonderful ways to calculate pi. My favourite is Buffon's Needle, which involves taking a box of matches and drawing a series of parallel lines at a distance of two matchsticks in length apart. You then toss the matches down and count the number of matches that cross the lines.

If you take the total number of matches tossed and divide by the number that cross the lines, the answer should be close to pi. So by collecting the data from enough tosses we should be able to get an estimate for pi.

An online video of the event will be available shortly at

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