How are rational numbers written as decimals?

Answer 1

To convert a rational number to a decimal divide the numerator by the denominator.

If the denominator contains any prime factor other than 2 and/or 5, the decimal will not terminate but end with one or more digits recurring. In this case it is either rounded or written with a dot over the first and last recurring digits (if only one digit recurs then a single dot is placed over that digit at the end of the decimal).

As it is not always possible to type the correct format with dots over recurring digits, I will often write the recurring digit(s) three times followed by an ellipsis (three full stops together) to mean "and so on", ie the decimal repeats.