What is a repeating decimal?

A repeating decimal is classified as a rational number. This is because it can be expressed as a fraction, where the numerator is an integer and the denominator is a non-zero integer. For instance, the decimal 0.666... can be represented as the fraction 2/3. The defining characteristic of repeating decimals is that they have a sequence of digits that continues indefinitely in a repeating pattern, which signifies that they can be precisely represented as a ratio of two integers.

In contrast, irrational numbers cannot be expressed as a simple fraction; their decimal expansions are non-repeating and non-terminating. Prime numbers are natural numbers greater than 1 that have no divisors other than 1 and themselves, while whole numbers are non-negative integers, starting from 0 and going up. None of these definitions apply to repeating decimals, which is why the correct classification is that they are rational numbers.