Roman number system of writing numerals is one of the earliest number system.

In Hindu Arabic numeral system 10 symbols are used to represent the numbers or numerals but in Roman number system 7 symbols are used to represent different numbers.

1 = I , 5= V, 10 = X , 50 = L, 100 = C, 500 = D, 1000 = M.

If a symbol is repeated one after the other, its value is added as many times as it is written.

For example :

III = 3

XXX = 30

CC = 200

The symbols I, X,C and M can be repeated maximum for 3 times.

For example :

C = 100 CC = 200 CCC = 300

M = 1000 MM = 2000 MMM = 3000

The symbols V,L and D can never be repeated in a Roman numeral.

If a symbol with a smaller value is written on the right side of a symbol with a greater value then, its value is added to the value of greater symbol.

For example

VI = 5 + 1 = 6

XII = 10 + 1 + 1 = 12

If a symbol with smaller value is written on the left side of a symbol with a larger value, then its value is subtracted from the value of greater symbol.

For example

IV = 5 – 1 = 4

IX = 10 – 1 = 9

The symbols V,L and D are never written to the left of a symbol of greater value.

Other numbers are made using some rules. All the rules of writing roman numbers have been explained in this video.