Lawrence Weinstein - Guesstimation: Solving the Worlds Problems on the Back of a Cocktail Napkin

How big IS it?

Numbers are thrown at us all the time. They are frequently used to scare us: Shark attacks doubled this year! or Dozens of lives could be saved by using infant car seats on airplanes! They are often used to tempt us: This weeks lottery prize is $100 million! They are certainly needed to understand the world around us: The average American produces 100 cubic feet of garbage every year! or Nuclear power plants produce tons of high-level radioactive waste!

You can make sense of these often confusing and sometimes contradictory numbers with just two tools: (1) an understanding of the meaning of large numbers and (2) an ability to make rough, common-sense, estimates starting from just a few basic facts. Well teach you these straightforward skills so you can better understand the world around you and better recognize numerical, political, and scientific nonsense.

You can also use these tools to further your career. Many top companies use estimation questions in job interviews to judge the intelligence and flexibility of their applicants [1]. Leading software firms, management consultants, and investment banks (for example, Microsoft, Goldman Sachs, and Smith Barney) ask questions such as Whats the size of the market for disposable diapers in China? How many golf balls does it take to fill a 747? and How many piano tuners are there in the world? [2, 3] Companies use these questions as an excellent test of the applicants abilities to think on their feet and to apply their mathematical skills to real-world problems.

These problems are frequently called Fermi problems, after the legendary physicist Enrico Fermi, whodelighted in creating and solving them. During one of the first atomic bomb tests, Fermi supposedly dropped a few scraps of paper as the shock wave passed and estimated the strength of the blast from the motion of the scraps as they fell.

In this book, we will help you develop the ability to estimate almost anything, from the amount of landfill space needed to the number of people in the world picking their nose at this instant. As there is no single correct way to analyze these questions, we will indicate some of the many paths to the right answer.

We will start with two short chapters on how to estimate and how to handle large numbers, and then well move on to the heart of the book: interesting questions (with lots of hints if you want them) followed by the answers on the other side of the page. The questions are divided into chapters, each focusing on a particular topic, such as energy and the environment, transportation, and risk. Each chapter will start with easier questions and work up to harder ones. The questions in will cover energy in its various forms. We will start with mountain climbing and go on to compare gasoline, chocolate chip cookies, batteries, the Sun, gerbils, windmills, and uranium.

The questions cover a large range of phenomena, from the simple to the complex and from the silly to the serious. We will figure out the answers to many fascinating questions, including the following:

• If all the people in the world were crammed together, how much space would we occupy?

• How many batteries would it take to replace your cars gas tank?

• Could Spider-Man really stop a subway car?

• How much waste do nuclear and coal electric power generators make per year?

• What does it really cost to drive a car?

• Which is more powerful per pound, the Sun or a gerbil?

• How much more cropland would we need to replace gasoline with corn-based ethanol?

All you will need to answer these questions is a willingness to think and to handle big numbers. We will remind you of the few scientific principles and equations you might need. You will be astonished at how much you can figure out starting with the knowledge you already have.