Rob EastawayMaths on the Back of an Envelope: Clever Ways to (Roughly) Calculate Anything

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.

I’ve just started a maths course and this book has given me ideas for at least getting a ball park figure before submitting my answersRecommended.

Read it on my kindle then bought a hardback copy for my kids to read and lend to all my friends. Explains a lot of the shortcuts that I already use and haven’t been able to explain well enough myself to my children.Good fun doing the “tests” too.

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.

Nice recreational maths book for light reading and interesting problems.