In this part . . .
Arithmetic with whole numbers is fine, but the world runs on more than whole numbers. In Part II, you find out every way to slice and dice a number.
Chapter 8 through 10 all deal with ways to work with a part of 1 (fractions, decimals, and percentages, respectively). Chapter 11 works with exponents, which help you express huge and tiny numbers in a more compact manner, and square roots, which help you find basic dimensions when you know areas.