# Roman Numeral

## Roman Numeral

Symbols used from the time of the Roman Empire until the end of the Middle Ages in Europe.

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