The Roman numeric system originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the late Middle Ages. Numbers in this system are represented by combinations of letters from the Latin alphabet. Today Roman numerals are based on seven symbols:

Symbol I V X L C D M

Value 1 5 10 50 100 500 1,000

Numbers are formed by combining symbols and adding the values, so II is two (two ones), XIII is thirteen (a ten and three ones), CCVII (two hundreds, a five and two ones) and MLXVI (a thousand, a fifty, a ten, a five and a one).

Symbols are placed in order from left to right, starting with the largest. However, in a few specific cases, to avoid four characters being repeated in succession (such as IIII or XXXX), subtractive notation is used: as in this table:

Number 4 9 40 90 400 600

Notation IV IX XL XC CD CM

I placed before V or X indicates one less, so four is IV (one less than five) and nine is IX (one less than ten)

X placed before L or C indicates ten less, so forty is XL (ten less than fifty) and ninety is XC (ten less than a hundred)

C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand).

Therefore XCV is 95 (ten less than a hundred plus five).

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