The rules as we now know them today governing the Roman numeral system had absolutely nothing to with the ancient Romans whatsoever because they were introduced during the Middle Ages and so as a result nowadays 599 and 219 are now considered to be DXCIX and CCXIX in Roman numerals which hardly lends themselves quite easily towards arithmetical operations but there exist historical evidence to suggest that the ancient Romans would have worked out the above calculations as in the following four formats:-
IDC+ICCXX = DCCCXVIII => (600-1)+(220-1) = 818
DLXXXXVIIII+CCXVIIII = DCCCXVIII => 599+219 = 818
IDC-ICCXX = CCCLXXX => (600-1)-(220-1) = 380
DLXXXXVIIII-CCXVIIII = CCCLXXX => 599-219 = 380
The above calculations were fairly simple and straightforward to work out but for more complicated calculations the Romans would have made use of an abacus calculating device.
QED
See answer to question: ' How do you add together 1666 and 1999 in two different ways using Roman numerals'
Both 1776 plus 444 added in two different ways will have sum of MMCCXX = 2220 and both 17,776 minus 444 subtracted in two different ways will have a difference of (XVII)CCCXXXII = 17,332
Roman numerals are entirely inappropriate for doing such calculations. I believe the people in Roman times did such calculations on an abacus or something similar - which is basically similar to converting them to the Arabic numbers we use. If you really want to do it in Roman numerals - which is basically NOT a good idea - you would have to keep the thousands, hundreds, etc. separate, and handle carry (for addition) and borrowing (for subtraction).
Nowadays 249 when converted into Roman numerals is now considered to be CCXLIX but the ancient Romans probably worked out the required calculations as follows:-MDCCLXXVI+ICCL = MMXXV => 1776+(250-1) = 2025MDCCLXXVI+CCXXXXVIIII = MMXXV => 1776+249 = 2025MDCCLXXVI-ICCL = MDXXVII => 1776-(250-1) = 1527MDCCLXXVI-CCXXXXVIIII = MDXXVII => 1776-249 = 1527For more complicated calculations the Romans would have made use of an abacus calculating device.QED
The rules as we know them today now governing the Roman numeral system had absolutely nothing to do with the Romans because they were introduced during the Middle Ages and as a result of these rules the equivalent of 1999 when converted into Roman numerals is now considered to be MCMXCIX which hardly lends itself quite easily for the purpose of mathematical operations but notwithstanding the aforementioned inasmuch that there exist credible evidence to support the premiss that the ancient Romans would have carried out the requested calculations as in the following formats:-MDCCCCLXXXXVIIII+DCLXVI = MMDCLXV => 1999+666 = 2665IMM+DCLXVI = MMDCLXV => (2000-1)+666 = 2665MDCCCCLXXXXVIIII-DCLXVI = MCCCXXXIII => 1999-666 = 1333IMM-DCLXVI is the same as the above because IMM = MDCCCCLXXXXVIIIIFor more intricate and complicated calculations the Romans would have made use of an abacus calculating device.QED by David Gambell
See answer to question: ' How do you add together 1666 and 1999 in two different ways using Roman numerals'
Both 1776 plus 444 added in two different ways will have sum of MMCCXX = 2220 and both 17,776 minus 444 subtracted in two different ways will have a difference of (XVII)CCCXXXII = 17,332
Roman numerals are entirely inappropriate for doing such calculations. I believe the people in Roman times did such calculations on an abacus or something similar - which is basically similar to converting them to the Arabic numbers we use. If you really want to do it in Roman numerals - which is basically NOT a good idea - you would have to keep the thousands, hundreds, etc. separate, and handle carry (for addition) and borrowing (for subtraction).
Since you ask how I would do it: I would forget about doing this in Roman; rather, I would convert everything to arabic numbers, which are much more appropriate for such calculations.
Under today's modern rules now governing the Roman numeral system the equivalent of 249 when converted into Roman numerals is now considered to be CCXLIX which does not lend itself quite easily to arithmetical operations but there exist credible evidence to suggest that the ancient Romans would have carried out the requested calculations as follows:-MDCCLXXVI+ICCL = MMXXV => 1776+(250-1) = 2025MDCCLXXVI+CCXXXXVIIII = MMXXV => 1776+249 = 2025MDCCLXXVI-ICCL = MDXXVII => 1776-(250-1) = 1527MDCCLXXVI-CCXXXXVIIII = MDXXVII => 1776-249 = 1527Note that in mathematics -(250-1) becomes -250+1 or as 1-250The above calculations were fairly simple and straight forward to work out but for more complicated calculations the Romans would make use of an abacus calculating device.QED
The rules as we know them today now governing the Roman numerals system had absolutely nothing to do with the Romans because they were introduced during the Middle Ages and as a result of these rules 1999 when converted into Roman numerals is now considered to be MCMXCIX which hardly lends itself quite easily for the purpose of arithmetical operations but notwithstanding the aforementioned inasmuch that there exist credible evidence to support the premiss that the ancient Romans would have worked out the requested calculations as in the following formats:-MDCCCCLXXXXVIIII+MDCCLXXVI = MMMDCCLXXV => 1999+1776 = 3775IMM+MDCCLXXVI = MMMDCCLXXV => (2000-1)+1776 = 3775MDCCCCLXXXXVIIII-MDCCLXXVI = CCXXIII => 1999 -1776 = 223IMM-MDCCLXXVI is the same as the above because IMM = MDCCCCLXXXXVIIIIThe above calculations were fairly simple and straightforward to work out but for more complicated calculations the Romans would have made use of an abacus calculating device.QED
The rules as we know them today now governing the Roman numerals system had nothing to do with the Romans because they were introduced during the Middle Ages and as result of these rules the equivalent of 999 converted into Roman numerals is now considered to be CMXCIX which hardly lends itself quite easily for the purpose of mathematical operations but there exist credible evidence to show that the ancient Romans would have worked out the requested calculations as in the following formats:-MDCCLXXVI+IM = MMDCCLXXV => 1776+(1000-1) = 2775MDCCLXXVI+DCCCCLXXXXVIIII = MMDCCLXXV => 1776+999 = 2775MDCCLXXVI-IM = DCCLXXVII => 1776-(1000-1) = 777MDCCLXXVI-DCCCCLXXXXVIIII = DCCLXXVII => 1776-999 = 777Note that in mathematics -(1000-1) becomes 1-1000 and that the above calculations were fairly simple and straightforward to work out but for more advanced calculations the Romans would have used an abacus calculating device.QED
Numerals are used for mathematical calculations. Mathematical calculations are used in science. This is the way Roman numerals related to Roman science.
Nowadays 249 when converted into Roman numerals is now considered to be CCXLIX but the ancient Romans probably worked out the required calculations as follows:-MDCCLXXVI+ICCL = MMXXV => 1776+(250-1) = 2025MDCCLXXVI+CCXXXXVIIII = MMXXV => 1776+249 = 2025MDCCLXXVI-ICCL = MDXXVII => 1776-(250-1) = 1527MDCCLXXVI-CCXXXXVIIII = MDXXVII => 1776-249 = 1527For more complicated calculations the Romans would have made use of an abacus calculating device.QED
The rules as we know them today now governing the Roman numeral system had absolutely nothing to do with the Romans because they were introduced during the Middle Ages and as a result of these rules the equivalent of 1999 when converted into Roman numerals is now considered to be MCMXCIX which hardly lends itself quite easily for the purpose of mathematical operations but notwithstanding the aforementioned inasmuch that there exist credible evidence to support the premiss that the ancient Romans would have carried out the requested calculations as in the following formats:-MDCCCCLXXXXVIIII+DCLXVI = MMDCLXV => 1999+666 = 2665IMM+DCLXVI = MMDCLXV => (2000-1)+666 = 2665MDCCCCLXXXXVIIII-DCLXVI = MCCCXXXIII => 1999-666 = 1333IMM-DCLXVI is the same as the above because IMM = MDCCCCLXXXXVIIIIFor more intricate and complicated calculations the Romans would have made use of an abacus calculating device.QED by David Gambell
c - cc = -c
When 9 is converted into Roman numerals it is IX which is an abridged version of VIIII and so the required calculations are as follows:-MDCCLXXVI+IX = MDCCLXXXV => 1776+(10-1) = 1785MDCCLXXVI+VIIII = MDCCLXXXV => 1776+9 = 1785MDCCLXXVI-IX = MDCCLXVII => 1776-(10-1) = 1767MDCCLXXVI-VIIII = MDCCLXVII => 1776-9 = 1767Note that in mathematics -(10-1) changes to 1-10QED