How can 1999 possibly be IMM in roman numerals when it is MCMXCIX?

Answer 1

In accordance with the rules laid down during the Middle Ages 1999 in Roman numerals works out as MCMXCIX but these rules were introduced centuries after the fall of the Roman Empire.

The Romans themselves would have probably calculated 1999 on a abacus counting device as MDCCCCLXXXXVIIII and by placing I to both sides of these numerals simplified them to IMM (-1+2000 = 1999)

Or alternatively they could have possibly worked out 1999 as IXCMMCX which gives a final result of IMM when positive and negative numerals are cancelled down. This method is achieved in the following manner:

1000 = M

1000+900 = CMM

1000+900+90 = XCMMC

1000+900+90+9 = IXCMMCX => IMM when cancelled down.

Both methods will give exactly the same result when converting any Hindu-Arabic numerals into Roman numerals.