How many people do you need in a room before there'll be a birthday in common? Why is 70 weird, and what can we do about it? How can 56 people eat 1 pizza's In 100 bite-size chapters of no more than three pages each, Adam Spencer gives each number, 1 to 100, its place in the limelight. For example, take 65. It's the constant of a 5 x 5 "magic square" — a square that contains the numbers 1 to 25, where all the rows and columns and each diagonal add up to 65. Elizabeth Taylor had 65 costume changes in Cleopatra. And sharks can travel up to 65 kilometers per hour (about 40 mph). After reading Adam Spencer's Book of Numbers, readers will never look at numbers the same way again.