This document discusses rational and irrational numbers within the real number system. It defines rational numbers as numbers that can be expressed as a ratio of two integers, such as fractions, decimals that terminate or repeat. Irrational numbers are numbers that cannot be expressed as a ratio of two integers, such as non-terminating and non-repeating decimals, square roots of non-perfect squares, and numbers like pi. The document provides examples of rational and irrational numbers and demonstrates how to plot irrational numbers on a number line based on their decimal expansions.