Let's start with I. In the Roman system, I has a value of 1. People think that the Roman numeral I developed from tally marks. We use only the letter I to write the first three Roman numerals just like we would write them using tally marks:
I = 1
II = 2
III = 3
This is pretty easy so far, right? You might be wondering why I didn't write IIII for 4. In fact, you may have seen the Roman numeral 4 written that way on a clock face. But in math, we follow a rule that says we should only repeat a letter three times. We follow this rule because otherwise Roman numerals could get very long and confusing - imagine writing the Roman numeral 100 by writing I 100 times!
Okay, it is time for the second letter we'll be learning. V has a value of 5 in the Roman System. We'll use V and I together to write the numbers from 4 to 8. You'll need to learn two rules to help you do this.
1. When a larger number is written in front of a smaller number, you add the values together. So, if you see the Roman numeral VI, you'll notice that the larger number (V, which has a value of 5) is written in front of the smaller number (I, which has a value of 1). That means VI is 5 + 1, or 6.
2. When a smaller number is written in front of a larger number, you subtract the smaller value from the larger. So, if you see the Roman numeral IV, you'll notice that this time the smaller number (I, which has a value of 1) is written in front of the larger number (V, which has a value of 5), This means that IV is 5-1, or 4.
Now you know enough to write the numbers from 4 to 8.
IV = 4
V = 5
VI = 6
VII = 7
VIII = 8
Why can't we write VIIII for the Roman numeral 9? Right, because we're following the rule that tells us not to repeat the same letter more than 3 times. You guessed it - that means it is time to learn our last letter!
The letter X has a value of 10 in the Roman system. How can we use the letter X to write the number 9?
Here's a hint : 9 is 1 less than 10.
Here's another hint : We'll use the letters I and X.
All right, one last hint : We'll use the rule that tells us when the smaller number is written in front of the larger number, we subtract the smaller value from the larger.
Have you got it?
Right, IX is the Roman numeral for 9. Here are the Romal numerals for 9 to 20:
II = 2
III = 3
IV = 4
V = 5
VI = 6
VII = 7
VIII = 8
IX = 9
X = 10
XII = 12
XIII = 13
XIV = 14
XV = 15
XVI = 16
XVII = 17
XVIII = 18
XIX = 19
XX = 20