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When X Always = 10

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Roman numerals are a collection of symbols that make up the number system that was used by the ancient Romans. Today, Roman numerals are more commonly used in titles, to number parts of works, in music theory, and on clock faces. Where do you see Roman numerals most often?

The Symbols

The Roman numeral system uses only seven symbols: I, V, X, L, C, D, and M. I represents the number 1, V represents 5, X is 10, L is 50, C is 100, D is 500, and M is 1,000. Different arrangements of these seven symbols represent different numbers. The numbers 1–10 are:

  • 1 = I
  • 2 = II
  • 3 = III
  • 4 = IV
  • 5 = V
  • 6 = VI
  • 7 = VII
  • 8 = VIII
  • 9 = IX
  • 10 = X

Forming the Numerals

Equating Roman numerals with the numbers you already know is just the first step. When you’re using them to write longer numbers, like years, there are a few guidelines to keep in mind.

You can add numbers together by putting the symbols in descending order from left to right. You’d add all of the symbols’ individual values together to get the total value. For example, XVI is 10 + 5 + 1, or 16. XXXIII is 10 + 10 + 10 + 1 + 1 + 1, or 33.

You can also subtract numbers from each other by placing a symbol with a smaller value to the left of one with a larger value. The value of the smaller symbol is subtracted from that of the larger symbol to get the total value, so IV is 5 – 1, or 4.

The subtractive principle has a few specific limitations. For instance, a numeral can only be placed in front of the two numerals that are closest to it in the Roman numeral system. That is, I can only be placed before V ( e.g. IV, or 4) and X (e.g. IX, or 9). It can’t be placed before L, C, D, or M. For example, in Roman numerals, 49 would be XLIX (50 – 10 = 40 and 10 – 1 = 9), not IL. Further, you can only place one smaller numeral in front of a larger one for subtractive purposes. For example, the correct way to write 8 is VIII, not IIX.

Use a bar over each symbol to multiply it by 1,000. For example, an X with a line over it is 10,000, while an M with a line over it means 1,000,000.

Titles and Names

Roman numerals are often used in royal titles. This is customary when there have been more than one rulers with the same name in the history of a given country. For example, in the title of the longest-reigning British monarch, Queen Elizabeth II. This differentiates her from the first Queen Elizabeth, who ruled during the mid- to late-1500s.

Sequences

Series of books, seasons of TV shows, and other sequential parts of larger works may use Roman numerals for numbering. For example, Into The Woods by John Yorke uses Roman numerals to break up the five acts, or sections, of the book. Livy’s The Early History of Rome uses numerals to organize the collection of 142 books.

Music

In music theory, Roman numeral analysis relies on these symbols for organization. Uppercase Roman numerals indicate a major triad, while lowercase symbols represent a minor triad. This style deviates from traditional Roman numerals, which don’t use lowercase letters.

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