Roman Numerals are represented by seven different symbols:
I, V, X, L, C, D, and M.
For example, 2 is written as II in Roman numeral.
12 is written as XII, which is X + II.
The number 27 is written as XXVII, which is XX + V + II.
Roman numerals are usually written largest to smallest from left to right.
However, the numeral for four is not IIII. Instead, the number four is
written as IV because the one is before the five we subtract it making four.
The same principle applies to the number nine, which is written as IX.
There are six instances where subtraction is used:
I can be placed before V (5) or X (10) to make
4 or 9 respectively.
X can be placed before L (50) or C (100)
to make 40 or 90 respectively.
C can be placed before D (500) or M (1000)
to make 400 or 900 respectively.