Rules of Roman Numerals
The Roman numeral system is an ancient additive-subtractive numbering system originated in ancient Rome. It uses seven letters of the Latin alphabet to represent values from 1 to 3,999.
1. Additive Principle
When a symbol appears after a larger (or equal) symbol, its value is added. E.g., VI = 5 + 1 = 6 and XX = 10 + 10 = 20.
2. Subtractive Principle
When a smaller symbol appears before a larger symbol, its value is subtracted. E.g., IV = 5 - 1 = 4 and IX = 10 - 1 = 9.
3. Repetition Limit
A symbol may not be repeated more than 3 consecutive times. Instead of IIII, write IV; instead of XXXX, write XL.