## Introductory Algebra for College Students (7th Edition)

The set of natural numbers is { 1, 2, 3, 4, 5, ... } . The set of whole numbers is { 0, 1, 2, 3, 4, 5, ... } The set of integers is {... , -4, -3, -2, -1,0, 1, 2, 3, 4,...} The set of rational numbers$: \displaystyle \frac{a}{b},\ b\neq 0$, and b integers Irrational numbers: are not rational (can not be written as $\displaystyle \frac{a}{b},\ b\neq 0$) Real numbers: all rational and irrational numbers. --- We count the number of students when we determine the size of a class. If there are no students, there is no class. The numbers used for counting are natural numbers, { 1, 2, 3, 4, 5, ... } The size of a class is a natural number.