Question: why is 49 xlix and not il?
Answer: On the face of it, IL and IC appear to follow the same subtractive principle as IV and IX, i.e. IL = L (50) - I (1) = 49. This is actually not valid. ... By these rules, the Roman numerals IL for 49 and IC for 99 do not work. The correct representation for 49 is XLIX, for 99 is XCIX.