Maths on the Back of an Envelope: Clever ways to (roughly) calculate anything
‘Another terrific book by Rob Eastaway’ SIMON SINGH ‘A delightfully accessible guide to how to play with numbers’ HANNAH FRY How many cats are there in the world? What's the chance of winning the lottery twice? And just how long does it take to count to a million? Learn how to tackle tricky maths problems with nothing but the back of an envelope, a pencil and some good old-fashioned brain power. Join Rob Eastaway as he takes an entertaining look at how to figure without a calculator. Packed with amusing anecdotes, quizzes, and handy calculation tips for every situation, Maths on the Back of an Envelope is an invaluable introduction to the art of estimation, and a welcome reminder that sometimes our own brain is the best tool we have to deal with numbers.
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Copyright
HarperCollinsPublishers 1 London Bridge Street London SE1 9GF
First published by HarperCollinsPublishers 2019
FIRST EDITION
© Rob Eastaway 2019
Cover design by Andrew Davis © HarperCollinsPublishers Ltd 2019 Cover photograph © Shutterstock.com
A catalogue record of this book is available from the British Library
Rob Eastaway asserts the moral right to be identified as the author of this work
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Source ISBN: 9780008324582
Ebook Edition © September 2019 ISBN: 9780008324599
Version 2019-08-30
CONTENTS
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PROLOGUE
HOW MANY CATS?
A few years ago, at a school event, I asked the audience of teenagers to submit some estimation questions that I would then attempt to answer live on stage. One pupil posed this simple question: ‘How many cats are there in the world?’
Cats are always a popular topic, so I took it on.
My thinking went like this:
Let’s assume that most cats are domestic.
Some people have more than one cat, but usually a household has only
