## Wednesday, 21 May 2014

### Numbers Are Forever by Liz Strachan

Reviewed by Chris Longmuir

I am no mathematician, in fact I’m probably like the teenagers described in the introduction to this book, and have to be ‘cajoled, diverted and entertained’. However, I do like puzzles, and there are puzzles in plenty in this book which is all about numbers and written by a mathematician. For example, ask someone to roll three dice and keep the result secret, this book will tell you how to work out how many spots were on each dice. Then there is the trick using words and numbers – the answer is always 4 – this book will tell you how it is done. A similar trick can be done with a secret number. I reckon these two alone would make a good party trick. Then there is the number puzzle where you always end up with 9 no matter what number you start with. Oh, and do you know how to make your calculator flash ERROR instead of giving you the answer? Just try dividing any number with 0, or zero if you prefer.

I also liked the snippets of information in this book. I discovered how to test whether a credit, debit, or any kind of card is valid by using a formula to count the numbers. The answer must be divisable by 10, otherwise your card is not valid or you’ve made a mistake in the counting. I also found out that Doctor Who used a sequence of happy prime numbers as a code to unlock a sealed door on a spaceship that is about to collide with the sun. I bet you didn’t know that! Meanwhile the humour ensures this is not a dry read. As Liz Strachan says the most brilliant mathematicians in the Stone Age were the ones who could count “One rock, two rocks . . . er . . . many rocks”.

This book is fascinating. It can be read to help with mathematics, and will show many quick ways to work out convoluted sums, or used as I did to find out the puzzles. It is written in a humorous style and is therefore entertaining. I reckon there’s something for everybody in this book.

Chris Longmuir