How can you tell if a decimal is repeating or terminating?

Answer 1

That depends how the decimal is defined. If you have a fraction, and convert it to a decimal:

* If the fraction, in simplest terms, only has the prime factors 2 and 5 in its denominator, the corresponding decimal number is terminating. This is related to the fact that 2 and 5 are the factors of 10 (the base of our decimal system). For example, a denominator of 2, 4, 5, 8, 10, 16, 32, 125, 625, 20, etc., will be terminating.

* If there is any other prime factor in the denominator, the corresponding decimal number will repeat periodically. This is the case with denominators such as 3, 6, 7, 9, 11, 12, 13, etc.