99 in Roman Numerals

What is 99 in Roman Numerals?

The number 99 in Roman numerals is XCIX.

99 is quite a difficult number to convert into Roman numerals, particularly if you are just starting out in trying to understand and learn about the Roman numbering system.

This is because it is a Roman numeral which requires to subtractive principle to be utilized. More information about this can be found on our Roman numerals page, but essentially what this means is that when a Roman numeral which is smaller in number is written before one that is larger, then the smaller one needs to be taken away (subtracted) from the larger one that comes after it.

And to complicate matters even further, the Roman numeral XCIX needs us to use this on not one, but two occasions!

Why is the number 99 written as XCIX in Roman Numerals?

To answer this question, first we need to know what the various Roman numeral letters represent. For the equation XCIX, the ones we need to translate are:

X = 10
C = 100
I = 1

As X (10) is written before C (100), it means that the smaller amount needs to be taken away from the bigger number. So, in this case, 10 needs to be subtracted from 100, which gives us 90.

Now that we have converted the first part, we need to move on to the second part, which again requires us to make use of the subtractive principle. In this case, I (1) is written before X (10), which tells us that 1 needs to be taken away from 10, giving us the number 9.

Essentially, what we have done is broken the Roman numeral equation of XCIX down into two separate parts. This method is actually one of the best ways to calculate Roman numerals and convert them into present-day numbers.

All we need to do now is put the two together... 90 plus 9 equals 99!

What would happen if the smaller numbers came after the bigger ones?

As an interesting aside, lets just say that the smaller numbers were written after the bigger ones, so that the equation became CXXI. What number would this Roman numeral convert to?

The answer is that, without a subtractive principle being required, the Roman numeral letters simply all get added together.

In this example, the sum would just be:

C (100) + X (10) + X (10) + I (1) which would give us the answer 121.

Math Questions Containing the Roman Numeral XCIX (99)

Let’s have a go now at some math problems which contain the Roman numeral for 99, XCIX:

1. What is XCIX plus L?

A relatively straightforward question to start off with. All we really need to find out is what the letter L represents, as we haven’t mentioned that one yet in this article.

The Roman numeral L equals the number 50. Now that we know that, all we need to do is add 99 to 50, which gives us our answer of 149 (or CXLIX in Roman numerals... remember the subtractive principle at the end for the IX!)

2. What is XCIX minus LIV?

This one is slightly more difficult as, unlike the question above where we just needed to find out what number one letter represented, this time we need to perform another Roman numeral conversion sum to find out what LIV is.

To work this out, we already know from Question 1 above that L equals the number 50, so that part is fine. We also know that I = 1 and V = 5, and that because I is written before V then I needs to be subtracted from V. IV is therefore the number 4, so adding it to 50 gives us the answer to LIV, which is 54.

Finishing off the sum is:

XCIX (99) minus LIV (54) = 45 (or XLV in Roman numerals... remember the subtractive principle at the start for the XL!)

3. What is XXIV multiplied by XCIX?

This sounds like a big number coming up potentially!

XXIV is another four letter Roman numeral that requires the subtractive principle, but this one shouldn’t be a problem for us as we have already found out what all of these Roman numeral letters represent and how the IV at the end is dealt with.

Taking the equation in two parts is the best way forward again for solving XXIV.

The first part of XX is easy; it is just X (10) plus X (10) which equals 20. Next, we know from the question above that IV is equal to the number 4, so the Roman numeral XXIV represents the number 24.

Now that we know this, we multiply 24 by our 99, which is... *gets calculator out*... 2,376.

How do we write 2,376 in Roman numerals? The answer is MMCCCLXXVI. That looks horrendous, being a whopping 10 letters long, but if you take the time to look at it more closely you’ll see that it is not actually that frightening or difficult to understand. In fact, even with 10 letters, there is actually no instance of the subtractive principle being needed, so you just have to add of those letters together!

We’ve seen them all already, apart from the Roman numeral M which is equal to 1,000. Now that we know that, the whole equation is simply:

M (1,000) + M (1,000) + C (100) + C (100) + C (100) + L (50) + X (10) + X (10) + V (5) + I (1) = 2,376. Phew! You can see now why Roman numerals can be fairly cumbersome when compared to our present-numbers that are based on Arabic numerals, especially with regards to long numbers such as this one.

4. What is XCIX divided by IX?

A much easier one to finish with. Using the subtractive principle again, we can work out that IX is equal to the number 9 (X (10) minus I (1) = 9)

This means that we can work out the answer to the question by just dividing 99 by 9, which gives us our answer of 11.

Incidentally, the number 11 in Roman numerals is XI, which is the opposite way round of writing IX. This is because for the number 9 the I is written before the X, meaning that 1 needs to be subtracted from 10, whereas for the number 11, written as XI, the 1 needs to be added to the 10 because the I comes after the X.

Roman Numerals in The News:

Hidden Roman Numerals Unearthed on the Historic Stone of Destiny