1. Pi (or π) is a number that helps describe circles. It links the width of a circle with its perimeter, or the radius of a circle with its area, or the width of a ball and its volume. It’s the same number no matter how big your circle is – about 3.14159265.

2. We celebrate Pi approximation day on 22 July because the date (22/7) looks like a fraction, and that fraction is very close to Pi. It’s not exactly Pi, though. Pi can’t actually be written as a division (or ratio) of two whole numbers – Pi is ‘irrational’.

3. Pi approximation day is one of two pi-related days in a year. United States mathematicians celebrate Pi day on March 14, or 3.14. If you get a calculator and do the sums, you’ll find that Pi approximation day (22/7) is a better approximation of Pi than Pi day (3.14)!

3 1/7. I’m going to make a pie to celebrate – you can too!

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