
Roman numeration system
The Roman numeration system evolved around 500 BCE. Just like other anscient numeration systems, it uses special symbols to represent numbers.
The basic Roman numerals are the followings. Study them and memorise them if you can. It could become handy one day
Any other roman numerals are found by combining these basic numerals
Examples:
1) 154 is equivalent to CLIIII in Roman numerals
2) 1492 is equivalent to MCCCCLXXXXII in Roman numerals
3) 3495 is equivalent to MMMCCCCLXXXXV in Roman numerals
Over time, two useful attributes were introduced that made the Roman numeration system very useful and efficient
The first one is the subractive principle
With the subtractive principle, Roman numerals can be combined or paired so that when reading from left to right, the values of the symbols in any
pair increase.
The value of the new pair is:
bigger number in the pair − smaller number in the pair
For instance, I can pair I and V to make IV and the value of this pair will be V − I = 5 − 1 = 4
I can pair C and D to make CD and the value of this pair will be D − C = 500 − 100 = 400
I can pair X and L to make XL and the value of this pair will L − X = 50 − 10 = 40
This subtractive principle will make the writting of examples 1), 2), and 3) a lot simpler
1)
CLIIII = CLIV
2)
MCCCCLXXXII
Instead of CCCC, we can pair C and D to get CD and CD = 400 as demonstrated above
Also, instead of LXXXX, we can pair X and C to make XC since XC still equal to 90
Replacing CCCC (in bold) by CD, we get:
MCCCCLXXXII = MCDLXXXXII
Replacing LXXXX by XC (in blue), we get:
MCDLXXXXII= MCDXCII
So, instead of using 11 symbols, we can just use 7 to represent the same number
3)
MMMCCCCLXXXXV = MMMCDXCV
The second one is the multiplicative principle
Basically, a horizontal bar above any number means 1000 times the number
Examples:

