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

A good breezy read despite the mathematical problems in some cases to solve. I loved the chapter at the end with more amorphous problems like how much methane gas do cows emit daily. Recommend everyone who would love to do a refresher on market sizing quick math fundamentals.

Fills a niche and is pleasant reading, even if one detects a fashionable anti-Conservative bias (keep your politics out of it, is my view). Arithmetic matters even if it's not glamorous, and this book confirms that.

Loved this book! Picked up some really useful tips and it actually felt as if my brain was getting switched on. (If you don't have an envelope handy, napkins work too!)One star dropped because there was a section at the end that was less interesting to me personally. It was about estimating, and assumed you already know or can estimate some things - like how long it takes to fly from London to Sydney, or that you can visualise a race track and, from that, estimate the width of a lane. I have no idea, and my brain thinks it's trivia, and refuses to remember it. If you already know some or all of this stuff, or if it appeals to you, then Rob shows you how you can use this info to make rough estimates about other things. It was still interesting to read though, even though I'd put my envelope down at this point.Plus I can now quote pi to 8 significant digits, which I couldn't before, so that's good! 😁

This book gives useful tools for making rough estimates. Often, very often actually, thats good enough. There is no point in being precise for the sake of it in many situations. When you accept that then you can increase your ability to detect BS. Well worth the read.

As an avid practitioner of order-of-magnitude calculations (e.g., to verify bills), usually without the benefit of a pen and envelope, I enjoyed reading this book. However, I found an annoying number of mistakes, even in some of the calculations. At first I kept a list, fully intending to mail it to the publisher, but as the mistakes became too numerous I gave up. A few examples:- p. 42: "43 x 5" should be "43 x 10", but more seriously: "430 / 2 = 115"... Really?- p. 48: "1200 .. divide by 100 .. 12%" - no, the answer is 12, not 12%- p. 74: "72 / 4 = 13 years"... Really?- p. 65: one example of sloppy editing: "the exactly the right answer".Well, maybe in edition number 1 + 1 = 42.

This book made me laugh out loud many times. The bit about Charlotte Dujardin winning the Olympic Dressage event in 2012 is hilarious, How can anyone's score come down to a margin of 0.001%! when the judges are making subjective choices. Another one is about how many cats there are in the world, but I won't give that one away! A friend said why do I need this when I have a calculator in my mobile phone, this is true, but how often does anyone get their mobile out to do a quick calculation that you can do in your head.This book will teach you quick and simple ways to do those calculations, for example - Litres to Pints, Kilometres to Miles, Kilograms to Pounds. It is written in a down to earth easy to read style but at the same time it will stimulate your interest in numbers and mathematics. i can thoroughly recommend it.