Which Roman numeral is incorrect?
LXXX
LXX
LX
LLX
Step 1: Remember the common Roman symbols and their values: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000.
Step 2: Some symbols can be repeated up to three times in a row. For example, III = 3 and XXX = 30 are OK.
Step 3: Other symbols — V, L, and D — should never be repeated. They are not written twice in a row.
Step 4: Look at the option LLX. It uses L two times in a row. That breaks the rule from Step 3.
Step 5: Because L cannot be repeated, LLX is not a valid Roman numeral. So the incorrect numeral is option D.