Maths on the Back of an Envelope: Clever ways to (roughly) calculate anything

by Rob Eastaway

Overview

‘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.

Product Details

ISBN-13:	9780008324599
Publisher:	HarperCollins Publishers
Publication date:	09/19/2019
Sold by:	HarperCollins Publishers
Format:	eBook
Pages:	208
File size:	4 MB

About the Author

Rob Eastaway has written or co-written twelve books, including the bestselling Why Do Buses Come in Threes? and Maths for Mums and Dads as well as What Is a Googly?, the acclaimed beginner’s guide to cricket. He is the Director of Maths Inspiration, a national programme of theatre-based lecture shows for 15–17 year olds that has reached over 150,000 teenagers since it began in 2004.

Rob regularly gives talks to all age groups in primary and secondary schools, appears on BBC Radio 4’s current affairs/ numbers programme More or Less, and works closely with National Numeracy, the national charity that campaigns for better adult numeracy.

In 2017, Rob received the Zeeman medal for excellence in communication of maths to the general public.

Table of Contents

Prologue: How Many Cats? 1

The Perils of Precision 5

Envelopes Versus Calculators 5

Spurious Precision 10

Variability 18

Sensitivity 22

Does this Number Make Sense? 28

The Case for Back-of-Envelope Thinking 31

Tools of the Trade 33

The Essential Tools of Estimation 33

Are You an Arithmetician? 34

Basic Arithmetic 38

Decimals and Fractions 44

Calculating with Powers of Ten 52

Key Facts 59

Zequals 61

Everyday Estimation 69

Estimation and Money 69

Estimating Size 78

Metric and Imperial Conversions 90

Estimation and Statistics 97

Spotting Trends 108

Figuring with Fermi 113

The Fermi Approach 113

Counting 116

What Are the Chances? 129

Energy, Climate and the Environment 146

Fermi for the Fun of It 158

Last Word: When the Robots take Over 175

The Countdown Conundrum 175

Appendix 181

Answers and Tips 187

Acknowledgements 200

Editorial Reviews

‘A delightfully accessible guide to how to play with numbers’ – Dr Hannah Fry, author of Hello World and The Mathematics of Love

‘Put aside those calculators and computers, and find a pen and piece of paper! In a collection of riveting tips and examples, Eastaway shows us amazing short-cuts to get rough answers to important questions. I still find it remarkable that 16% of 25 is exactly the same as 25% of 16!’ – Professor Sir David Spiegelhalter, author of The Art of Statistics

‘Another terrific book by Rob Eastaway’ – Simon Singh

‘Packed with fun examples and fresh ideas. I thought I was on top of this subject, but I learned a lot’ – Tim Harford

‘A joyful primer about the lost art of calculating without a calculator’ – Guardian

From the Publisher