Roman numerals are used always in outlines, sometimes on gravestones and always on copyright dates. It's a good piece of information to know. I-1, II-2, III-3, IV-4, V-5, VI-6, VII-7, VIII-8, IX-9, X-10, XI-11, XV-15, XX-20, XXX-30, XL-40, L-50, LX-60, LXX-70, LXXX-80, XC-90, C-100, D-500, M-1000.
