With difficulty because new rules governing the Roman numeral system were introduced during the Middle Ages and as a result of these new rules the way we work out Roman numerals today are different to the way that the Romans actually did themselves but the methodical Romans would have probably totalled these numerals in the following logical manner:
M+CM = CMM
CMM+XC = XMM
XMM+IX = IMM
IMM+XI = MMX = Total
And when converted into Hindu-Arabic numerals:
1000+900 = 1900
1900+90 = 1990
1990+9 = 1999
1999+11 = 2010 = Total
Note that the above numerals are fairly simple to work out and so for any complicated calculations the Romans would have used an abacus counting device.
IVI has no meaning in Roman Numerals. IV is 4 V is 5 VI is 6 IVI does not follow the rules of how Roman Numerals work.
Arabic numerals are simpler to work with mathematically.
Tradition and so as to disguise the year when the movie was made because most people can't work out Roman numerals.
The date can't be expressed in Roman Numerals since it's incompatible with that number system. You can possibly work out with only numbers, such as 2 or 11.
Roman numerals:IX*IX = LXXXILXXXI/III = XXVIIXXVII+LXXIII = LXXXXVIIIII => CArabic numerals:9*9 = 8181/3 = 2727+73 = 100
IVI has no meaning in Roman Numerals. IV is 4 V is 5 VI is 6 IVI does not follow the rules of how Roman Numerals work.
Arabic numerals are simpler to work with mathematically.
Because most moviegoers can't work out Roman numerals and so they are unable to know in what year the movie was made.
Tradition and so as to disguise the year when the movie was made because most people can't work out Roman numerals.
The date can't be expressed in Roman Numerals since it's incompatible with that number system. You can possibly work out with only numbers, such as 2 or 11.
Today we write out 1999 in Roman numerals as MCMXCIX because of changes made to the rules governing the Roman numeral system during the Middle Ages and to add these numerals to MDCCLXXVI is almost impossible. But the Romans themselves would have calculated 1999 on an abacus counting device as MDCCCCLXXXXVIIII and probably simplified them to IMM by placing I to both sides of the numerals. So: MDCCLXXVI + (-I+MM) = MMMDCCLXXV (3775)
Roman numerals:IX*IX = LXXXILXXXI/III = XXVIIXXVII+LXXIII = LXXXXVIIIII => CArabic numerals:9*9 = 8181/3 = 2727+73 = 100
Wikipedia covers this topic extensively. I added a link below.
Under today's rules we write out the equivalent of 29 into Roman numerals as XXIX But under the Roman rules 29 was XXVIIII *By roman rules I assume you mean Roman Numerals. Romans wrote out 29 as XXIX, the same way they work today.
It is: CMLXVII which means -100+1000+60+7 = 967
Cmxcix + xiv + mcmlxxxvii = mmm. It should be all in capital letters, but the system changed them.
We still use Roman numerals to a certain extent today but the Roman numeral system was replaced by the Hindu-Arabic numeral system because it contained a zero symbol thus making arithmetical operations a lot easier whereas the Roman numeral system has no zero symbol and mathematical operations were much more difficult.