A rational number can be written as p/q where p and q are integers and q is not equal to 0. Rational numbers include whole numbers, natural numbers, and integers. Examples of rational numbers are -25, 1/2, and 1/4. An irrational number cannot be written as p/q and has a non-terminating, non-recurring decimal expansion like 0.10110111011110111110. The decimal expansion of a rational number is either terminating or non-terminating repeating, while an irrational number always has a non-terminating, non-recurring decimal expansion.