# Roman Numerals

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Roman numerals are expressed by letters of the alphabet and are rarely used today except for formality or variety. There are four basic principles for reading Roman numerals:

- A letter repeated once or twice repeats its value that many times (XXX = 30, CC = 200, etc.).
- One or more letters placed after another letter of greater value increases the greater value by the amount of the smaller (VI = 6, LXX = 70, MCC = 1200, etc.).
- A letter placed before another letter of greater value decreases the greater value by the amount of the smaller (IV = 4, XC = 90, CM = 900, etc.). Several rules apply for subtraction: (a) only subtract powers of ten (I, X, or C, but not V or L); (b) only subtract one number from another; (c) do not subtract a number from one that is more than 10 times greater (that is, you can subtract 1 from 10 [IX] but not from 20—there is no such number as IXX).
- A bar placed on top of a letter or string of letters increases the numeral's value by 1,000 times (XV = 15, = 15,000).

Letter | Value |
---|---|

I | 1 |

II | 2 |

III | 3 |

IV | 4 |

V | 5 |

VI | 6 |

VII | 7 |

VIII | 8 |

IX | 9 |

X | 10 |

XX | 20 |

XXX | 30 |

XL | 40 |

L | 50 |

LX | 60 |

LXX | 70 |

LXXX | 80 |

XC | 90 |

C | 100 |

D | 500 |

M | 1,000 |

5,000 | |

10,000 | |

50,000 | |

100,000 | |

500,000 | |

1,000,000 |

World's Largest Known Prime Number | Numbers and Formulas | Mean and Median |