Free interactive math game: Valid Roman? — IIII — yes or no?. Part of the Roman Numerals category on MathKite.
Taken from the generator that powers this exercise. A fresh set appears every time the page is opened, and the printable worksheet holds ten of them.
Deciding whether a Roman numeral is written correctly.
Check the rules: no symbol repeats more than three times, V, L and D never repeat, and only I, X and C may be used for subtraction.
VX is invalid, because V is never used for subtraction.
Accepting anything that can be read. A numeral has to be written in the standard way, not just be understandable.