Guesstimation: Solving the World's Problems on the Back of a Cocktail Napkin by Lawrence Weinstein and John A. Adam, illustrated by Patty Edwards (Princeton University Press, Princeton, 2008) is a book about estimation. The book doesn't contain much of an introduction on how to make estimates (other than mentioning that, for rough estimates such as the ones in this book, your guess doesn't have to be exact, only within the right order of magnitude, and, that if things look too complex, to break the problem up). Instead, the book jumps straight into making estimates, with most of the first estimates being ones for which exact data are available to check. While I might have appreciated a longer introduction to estimation, the best way for someone to improve their skills as an estimator is probably to make estimates and to check them afterwards, and this is how the book starts.

The book continues in this manner, consisting of about 80 questions or so, with the question posed on one page and an estimate to the answer given on the next page or two. There are about 80 questions or so in the book. These range from the frivolous ("How long would it take a running faucet to fill the inverted dome of the Capitol?") to ones that explore important issues that we are facing now ("How much more farmland would America need to farm to grow corn for enough ethanol to completely replace the gasoline used in all of our cars?"; "What fraction of the US land area would be needed to supply the US electrical energy needs with solar energy?") or in the future ("What is the kinetic energy of a meteorite 1 kilometre in diameter when it hits the earth?"; "How many tons of fuel will it take to get a spaceship from Earth to Alpha Centauri?"), to estimates that can help readers make smart decisions in their own lives ("What is the risk of dying per mile in an automobile compared with an airplane?").

The each question and its estimated answer takes only a few pages and could easily be made part of a classroom discussion or something similar. Each question is illustrated (the illustrations are by Patty Edwards) and the illustrations are unique and generally look pretty good.

In today's world, people are being bombarded by numbers and other information that requires numbers to be understood, and so having number sense is more important than ever. An important part of number sense is estimation, to be able to have a rough sense of quantity and magnitude, and to be able to quickly come up with a rough answer to a problem. With that in mind, I would highly recommend Guesstimation, as someone who puts effort into reading the book can improve their estimation skills, gain a better understanding of real-world problems, and gain the skills to apply estimation to other real-world problems they may face.

**Rating:** 9/10