Roman Numerals: The Rules 

There are three basic rules to remember:

1. No symbol is used more than 3 times in a row:

2. If a symbol appears after a larger or equal symbol, it is added to it:

Note: This works in all cases except `VV`. The symbol `X` is used to represent the number 10 therefore `VV` is not needed.

3. When the left-hand symbols are smaller than the right, subtract them from the right-hand symbol:

Note:
We can only subtract one character from another, so `IIX` would not be one and one from ten = 8.
Instead, to get `8` we would have to use `VIII` meaning `5+1+1+1=8`.

We can start counting and apply the rules we learnt using the sentence:

'I Value Xylophones Like Cows Do Milk'.
`I=1`,  `V=5`,  `X=10`,  `L=50`,  `C=100`,  `D=500`,  `M=1000`

1. `I`
   
   
2. `II`
   
   
3. `III`
   
   
4. `cancel(IIII)` – No symbol is used more than 3 times.
   `IV` (1 from 5 = 4) – when left is small and right is bigger, subtract left from right-hand figure.
   
   
5. `V`
   
   
6. `VI` (5 add 1 = 6) – If a symbol appears after a larger or equal figure it is added.
   
   
7. `VII` (5 add 1 add 1 = 7) – If a symbol appears after a larger or equal figure it is added.
   
   
8. `VIII` (5 add 1 add 1 add 1 = 8) – If a symbol appears after a larger or equal figure it is added.
   
   
9. `cancel(VIIII)` – No symbol is used more than 3 times.
   `IX` (1 from 10 = 9) – when left is small and right is bigger, subtract left from right-hand figure.
   
   
10. `X`

This pattern continues for every number.