Two fathers and two sons leave town. This reduces the population of the town by three. True? Yes, if the trio consists of a father, son, and grandson. This entertaining collection consists of more than 200 such riddles, drawn from every branch of mathematics. Math enthusiasts of all ages will enjoy sharpening their wits with riddles rooted in areas from arithmetic to calculus, covering a wide range of subjects that includes geometry, trigonometry, algebra, concepts of the infinite, probability, and logic. But only an elementary knowledge of mathematics is needed to find amusement in this imaginative collection, which features complete solutions and more than 100 black-and-white illustrations. "Mr. Northrop writes well and simply. Every so often he will illuminate his discussion with an amusing example. While reading a discussion of topology, the reviewer learned how to remove his vest from beneath his jacket. It works every time." -- The New York Times