4.2 Roman number system (Lesson 10)

Roman number system, originating in ancient Rome, was developed around 500 B.C. Roman numerals are still used today in numbered lists, clock faces, page-numbering, dates and so on.

A clock face

Credit: Wikipedia

The following are the seven symbols of Roman numerals:

Number are formed from a combination of these symbols under the following rules:

1. I, X, C and M can be repeated up to three times.
2. When a letter is repeated two or three times, add their values up. For example, "III = 1+1+1 = 3".
3. V, L and D cannot be repeated.
4. If a letter needs to be repeated four times, instead use this letter preceding one of the two next larger values to indicate the subtraction. For example:
   1. To represent 4, don't write IIII, use IV (5 is subtracted by 1)
   2. To represent 9, don't write VIIII or VIV, use IX (10 is subtracted by 1)
5. Groups of symbols are arranged in descending order from left to right. For example, suppose we want to represent "1997" and "2046". We represent them in Roman numerals as follows:

An example of modern day use of Roman numerals:

Year in Roman numerals

Credit: Wikipedia