# Seven Roman Numerals

You know that 2 + 2 = 4. But do you know that ii + ii = iv?

The numbers that we normally use (1, 2, 3 etc) are called "Arabic numerals". But we sometimes use another system for writing numers - "Roman numerals". The Romans used letters of the alphabet to represent numbers, and even today you will occasionally see this system used for page numbers, clock faces, dates of movies etc.

There are 7 letters used for Roman numerals:

I = 1

V = 5

X = 10

L = 50

C = 100

D = 500

M = 1000

In general, letters are placed in decreasing order of value, eg XVI = 16.

Letters can be repeated one or two times to increase value, eg XX = 20, XXX = 30.

Letters cannot be repeated three times, so XXXX is not used for 40. In this case, XL = 40 (50 minus 10).

Here are two examples:

- The Introduction is on page vii.
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