Because if XC = 90 and 9 = IX then it surely follows that XC+IX = XCIX in the same way that 90+9 = 99 but this is inconsistet with the real facts which are:-
Fact I: XC+IX = IC because (100-10)+(10-1) = (100-1)
Fact II: The Latin word for IC is 'undecentum' meaning one from a hundred
Fact III: More convincing evidence is available
Fact IV: XCIX for 99 is wrong and IC is correct
Fact V: Numerals are calculated differently today than in Roman times
In todays modern notation of Roman numerals they represent 99
99
The Roman numerals X-XCIX represent 10-99
99
The number 49 in Roman numerals is XLIX and the number 99 in Roman numerals is XCIX
In todays modern notation of Roman numerals they represent 99
49.5 = SL in Roman numerals
99
The Roman numerals X-XCIX represent 10-99
99
The number 49 in Roman numerals is XLIX and the number 99 in Roman numerals is XCIX
The number 99,989 can be represented by the Roman numerals (XCIX)CMLXXXIX
The number 99,989 can be represented by the Roman numerals (XCIX)CMLXXXIX
99+1056 = 1155 or MCLV in Roman numerals Today we write out 99 in Roman numerals as XCIX but the Romans themselves would have probably wrote it out simply as IC (-1+100 = 99)
C=100 X=10 I=1 So it is 10 before 100 (=90) plus 1 before 10 (=9) . Thus the answer in ARABIC numerals is "99", while of cause XCIX in ROMAN numerals is "XCIX"
XCIX is the modern standard for 99.
XCIX - XIX = LXXX