Looking at the roman numerals, it looks like doing arithmetic in that format will be a nightmare. But basic arithmetic—addition and subtraction—is pretty easy. Addition and subtraction are simple, and it’s obvious why they work. On the other hand, multiplication with roman numerals is difficult, and division is close to impossible. It’s worth noting that while scholars did teach arithmetic this way, most everyday calculations were done in Roman times with a Roman abacus, which works much more like our modern number system does.
To add two roman numerals, you do this:
Convert any subtractive prefixes to additive suffixes. So, for example, IX would be rewritten to VIIII.
Concatenate (or link together) ...