Roman Numeral

Today, Roman numerals are mainly used to write the century (XIX century, XX century… ) or to number the chapters or lessons of a book (chapters I, II, III, etc.). The names of kings and queens use Roman numerals (Louis XIV, Charles X … ), so teaching about the arts and history often uses this type of numbering. Finally, it’s not uncommon to find Roman numerals on a clock or wristwatch.

• Roman numerals are composed of seven capital letters that correspond to numerical values.
  

  I	V	X	L	C	D	M
  ↓	↓	↓	↓	↓	↓	↓
  1	5	10	50	100	500	1000

• Like Arabic numerals, Roman numerals are written from left to right.
• In this system, the numbers are composed:
  • By addition, by recording the numerals with lesser or equal values to the right of the numerals with greater values:
    XIII : 10 + 3 = 13
    MCL : 1000 + 100 + 50 = 1150
  • By subtraction, by recording the numerals with lesser values to the left of the numerals with greater values:
    IV : −1 + 5 = 4
    XL : −10 + 50 = 40
    CMXCIX : (−100 + 1000) + (−10 + 100) + (−1 + 10) = 999
    The numeral I can only be subtracted from V or X; the numeral X can only be subtracted from L or C; the numeral C can only be subtracted from D or M.
  • By multiplication, by placing a horizontal line above the Roman numeral to indicate that we are multiplying it by 1000:
    \(\overline{\textrm{V}}\) = 5 000
    \(\overline{\textrm{X}}\) = 10 000