Guesstimation is a delightful and useful exercise in making quick educated, albeit rude - within a factor of 10, estimates. The term has been around from the 1930s and is often associated with the name of the legendary physicist Enrico Fermi. "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." The term has been popularized in 2008 by Lawrence Weinstein and John Adam with the book Guesstimation. Now - four years later - Weinstein had a sequel out, Guesstimation 2.0. As the author writes in the Preface, "This book continues where the popular and widely reviewed Guesstimation leaves off." Perhaps significantly, the last chapter of Guesstimation listed Unanswered Questions, while the sequel features no such ending.
I estimate that eleven chapters of the first book and nine of the second answer about 200 curious (but not consistently important) questions the variety of which would satisfy many a delicate taste and diverse interests. The question/hints/answer combinations take about 3-4 pages each and, with rare exceptions, could be browsed independently. Occasionally, the author refers to the notes on the cuffs of a shirt made while reading earlier chapters. Other than that, the books could be opened and read starting at a random page.
How useful a guesstimation skill might be? Here's a stark example. A 2-page effort easily confirmed a 120-page 2011 study by the Environment Agency of England which showed that conventional plastic bags have much less overall impact on the environment than the alternatives (biodegradable plastic, paper, or reusable cotton bags.)
How many miles per gallon would a human achieve if we could metabolize gasoline? About 300 miles. Do you care for this silliness? You may not, but you should. The fact is that fat and gasoline contain almost the same amount of chemical energy, meaning that "we need to walk dozens of miles to burn off a single pound of fat."
How much energy does it take to transport 1 ton of cargo across the United States by truck? It'll take about 25 gallons of diesel fuel (about six times more efficient than a car.) Taking the distance between Los Angeles and New York to be about 2500 miles, the estimate shows that a truck needs 1 gallon of fuel to transport 1 ton over the distance of 100 miles. On the other hand (and this is a real world example for which I am grateful to Linda Fahlberg-Stojanovska), trains can move a ton of freight nearly 500 miles on a single gallon of fuel - five times more efficiently.
Well, there is no use in attempting to describe all 200 (an estimate) questions or to tell you which one I liked the most. There are truly enough of them to satisfy any taste and even more to show convincingly how useful the guesstimation skill is. The books do a wonderful jobs at helping the reader to master the craft.