As easy as pi

Conversation with someone you don't know earlier this week:

R: Did you know that, if you write each of the first three odd numbers down twice like this, 113355, and then move the second three above the first three to get a fraction, you get 355÷113?
X: So what?
R: Work it out on your calculator. What do you get?
X: 3
R: No, don't round it down. Read it out in full.
X: 3.1415929
R: Isn't that cool?
X: What the hell are you talking about?
R: Doesn't that number ring a bell?
X: Nope. Should it?
R: It's a very close approximation to the number pi. It's miles better than 22÷7.
X: What the hell is pi?
R: WHAT?! You must have heard of pi, it's one of the most important numbers in mathematics!
X: Oh, I've heard of it all right, but I don't know what it means. I was never any good at maths at school. Why is pi so important, then?
R: It's the number you get when you divide the circumference of a circle by its diameter.
X: Why the HELL would I need to know that?
R: Well, it's really important. Suppose you were going to paint a circular door, for example…
X: Where would I get a circular door?
R: It doesn't matter. Just suppose you were going to paint one. How would you know how much paint to buy?
X: I'd just buy five litres. That would be plenty.
R: …Ok, bad example, forget about the door. Imagine that teapot over there was a perfect sphere two feet across…
X: Can't I imagine a cube instead? They're easier.
R: But you don't need pi for cubes. Pi is for circular stuff.
X: Oh, I see, pi doesn't work on cubes—IT'S JUST A BIG CHEAT!
R: No it isn't. Pi makes it easier to do calculations with circles. That's the whole point! So imagine you've got this sphere two feet across and you wanted to fill it with water. How much water would you need?
X: I wouldn't need to work it out. I'd just fill it from the tap.
R: Yes, but if you did need to work it out, how many cubic feet of water would you need?
X: I suppose you're going to say pi.
R: Well, almost. You'd actually need four-thirds pi cubic feet.
R: NO! That's the volume of a sphere: four-thirds pi times the cube of its radius.

X is right of course. I have never needed to use pi outside my school maths homework—even though I can still recite it to 22 decimal places (nerdish schoolboy's trick).

Mind you, did you hear about that Japanese bloke the other week who recited pi to 83,431 decimal places?



HOLY CRAP!!! I PROMISE I didn't fix this… I just read on Wikipedia that today (22/7 in British date format, geddit?) is Pi Approximation Day.

Of course, you realise this proves that the paranormal is real, and there really is a god.

[Actually, there are two Pi Approximation Days (see Wikipedia article), so the odds of my publishing this particular item on one of them is 2 in 365 (or 1 in 182½). Hardly amazing, if you think about it—but still rather pleasing.]

Richard Carter

A fat, bearded chap with a Charles Darwin fixation.


  1. Either you are taking the Pi, or (judging from your photo) you ate them all!

  2. Did you know (I would not he surprised to find that you did) that Einstein was born on US Pi day - March 14 in the US is of course 3.14

    Don't know whether it is true, but there was supposedly a basic (or possibly BASIC, but I don't think so) programming manual which was harping on about using variables defined at the start of your code rather than reciting values of constants repeatedly throughout. The example given used "PI" which it defined as 3.14159265, or whatever, and there was a comment under the example that this made the code easier to amend "if the value of pi should change". After all -you have to prepare for every eventuality!

Leave a comment

Your email address will not be published. Required fields are marked *