Roman numerals are a numeral system which was used in Ancient Rome. It uses letters instead of numbers to represent values. You may have seen Roman numerals on clocks and on TV or film credits.

Roman numerals get nine by putting I, which equals 1, before X, which equals 10, to essentially indicated 10-1=9. For comparison, when I appears after X, as in XI, that indicates 10 + 1 ...

Unlike many other ancient systems, Roman numerals are still in use today ... D and M — stand for the numbers 1, 5, 10, 50, ...