## 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. --- A person can have no pets, so 0 is in the set. If the person has pets, we can count them. The set used for counting is the set of natural numbers, So, we have zero and the natural numbers... which is the set of whole numbers.