It represents number with letters (X, I, L, etc).
- One = I
Two = II
Nine = IX
Twelve = XII
Twenty-two = XXII
However, in the current era of maths computation, we have chosen to use the Hindu-Arabic ways of number presentation. This is now the accepted and standardised way in our number system.
But why the change?
Other than for some cosmetic and artistic applications, roman numbering are seldom used nowadays. The roman numeral is disadvantaged in that it requires more characters to represent some numbers.
An example is the number 28.
Roman numeral is XXVIII (6 characters needed).
Hindu-Arabic numeral is 28 (2 characters only!).
Its disadvantage handicaps the printing industries in that more printing hard characters are needed to represent the same number. More efforts and paper space are needed. Slowly, with times, printers were forced to switch to the more efficient way of using the Hindu-Arabic numerals.
Another disadvantage of roman numeral is that they are hard to mathematically operate upon. Simple addition, subtraction, multiplication and division are not done as simply as that of the Hindu-Arabic. Cautious and taxing steps of solving maths has to be taken care when using roman numerals.
Try adding VIII + XXVIII compared to 8 + 28. We need to count the "I"and "X" to add the roman numbers and that is only for 2-number addition!
With times, therefore, roman numerals are phased out in favour of the easily presented Hindu-Arabic numerals. This is the development of maths numeric.
Who knows the Arabic numberical system may one day be replaced by a better simplified system!