What’s XCX? And Other Roman Numerals!

by Rosemarie Hardison
xcx roman numeral

Like many other traditions that have survived to the present day, Roman numerals are retained for their touch of gravitas rather than any practical use they may have.

This becomes clear when we reflect back on our math classes. The older we got and the more complex arithmetics became, the rarer Roman numerals were used in the classroom.

Still, Roman numerals are used in a variety of contexts, such as in music theory, some clocks, and even movies.

Luckily, picking up Roman numerals is easy. So in this article, I’ll give you a rundown on Roman numerals and how they work. But before we get into that, let’s take a look at the peculiar XCX Roman numeral.

What Is XCX in Roman Numerals?

The short answer is that XCX isn’t a Roman numeral. While it’s certainly made of Roman numerals, it’s what’s considered an invalid Roman numeral.

Why XCX Is an Invalid Roman Numeral

There are a few rules to follow when writing Roman numerals. Breaking any of those rules renders a Roman numeral invalid, which is exactly what XCX did.

What renders XCX invalid is the rule that states a letter used as a subtraction modifier can’t appear again in the Roman numeral string.

In XCX, X (10) and C (100) are considered a group of numerals in subtractive notation. That means C – X = 90 or XC = 90.

If you add another X to the numeral string, you’d be adding back the ten that was subtracted from XC. However, if you were to add IX to XC, for example, you’d get a valid Roman numeral that follows all of the rules for writing a Roman numeral. XCIX = 99.

Still, going through and learning all the Roman-numeral rules can get frustrating very quickly, especially if you encounter a group of letters that’s somewhat exaggerated, such as MMMDCCXXIV.

Fortunately, an online calculator like numere-romane lets you convert from Roman to Arabic numerals and vice versa. However, its best feature, in my opinion, is that when you convert an invalid Roman numeral, it offers you a brief explanation of why it’s invalid.

List of Roman Numeral Meanings

Roman numerals are derived and formed from the Latin alphabet. Thankfully, there are only seven letters that we need to memorize.

  • I = 1
  • V = 5
  • X = 10
  • L = 50
  • C = 100
  • D = 500
  • M = 1000

How To Write Roman Numerals

Now that we’ve got the basics out of the way, let’s get into the nitty-gritty of how to write Roman numerals.

  1. You can’t write more than three of the same letters to express a number. So I = 1, II = 2, and III = 3, but 4 is written as IV.
  2. V, L, and D can’t be repeated even once to form a number, as they’re 5, 50, and 500 respectively. It appears that 5 prefers some personal space.
  3. Lower value Roman numerals placed on the left of larger ones are subtracted. That’s why 4 = IV and 9 = IX.
  4. As long as the leftmost letter is bigger than the following ones, the rest is simply added to it. So, 6 = VI and 12 = XII.
  5. As a result, I, X, and C are the only letters that we can subtract with.

Of course, there’s more to writing Roman numerals than those few rules, but they’re the most essential of all.

In Summary

Roman numerals have no practical use in our world today. Still, they certainly haven’t lost their appeal to countless people out there.

Picking up Roman numerals will help you share in the appreciation many have for this relic of the past.

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