Textbook in PDF format

Fun with numbers — really. 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? Mow can 56 people eat 1 pizza? In IOO bite-size chapters of no more than 2 pages each, Adam — a regular guy — gives each number, 1 to TOO, its place in the sun. 65? The constant of a 5 x 5 "magic square" — a square which contains the numbers l to 25, where all the rows and columns and each diagonal add up to 65. And Elizabeth Taylor had 65 costume changes in "Cleopatra."