Rule 1 – Repetition of a Roman Numeral means addition.
- Only letters I, X, C, M can be repeated.
- No letter can be repeated more than 3 times.
- Letter V, L, D are never repeated.
Rule 2 – When a smaller numeral is placed on the left of the larger numeral, it means Subtraction.
- I can be subtracted from V and X only.
- X can be subtracted from L and C only.
- C can be subtracted from D and M only.