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The rational numbers are the set of all numbers that can be expressed as fractions with integers in both the numerator and denominator. For example:

As you can see, the set of rational numbers includes all the integers, because every integer can be expressed as the numerator of a fraction with 1 in the denominator.

The set of rational numbers is closed under addition, subtraction, multiplication, and division.

Points on the number line that cannot be expressed as fractions — such as , , and — are called the set of irrational numbers.