10 May 2011

Proof of why a transposition error is always divisible by 9

Here's a little proof I knocked up over the weekend. Sorry it's in a picture format, the platform on which this blog is based can't deal with simple mathematical symbols, so I had to convert a document into a couple of pictures. If you click on the pictures, you should be able to see a larger version of each of the two pages of the proof.


  1. Please note, there is a deliberate error in here, so if you copy it verbatim it won't be watertight. If you want to correct it, you first have understand the error. ;-)

  2. Anonymous13 July, 2011

    Do you know who first made this known or who discovered the transposition error rule of divisible by 9?

  3. Sorry, no idea on that one. It just seems to be "one of those things."