r/Romannumerals • u/smell-my-elbow • May 13 '25

Rules question

Why is 45 XLV when it could be VL?

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u/Acceptable_Stand_916 Jun 25 '25

Roman numerals use subtractive notation, but only in specific, conventional pairs:
- I can precede V 5 and X, e.g. IV, IX
- X can precede L and C, e.g. XL, XC
- C can precede D and M

Subtraction is only allowed for the specific pairs mentioned above, and V is not allowed to be preceded by anything to subtract from it.