CMXXI in Roman Numerals

Ancient Romans discovered that counting fingers could get very complicated after 10. So, to overcome the complexity, the Roman numeric system was developed. This was widely used throughout Europe as a standard writing system until the late Middle Ages.

Seven symbols are used to represent numbers in the Roman numeric system — I, V, X, L, C, D, and M. The numerals are made up of different combinations of these symbols. CMXXI in Roman numerals can be written in number form by adding and subtracting the values of each Roman numeral, i.e., CMXXI = 921.

Let us learn more about the Roman numeral CMXXI, how we write them, the mistakes we usually make, and ways to avoid these mistakes.

When writing Roman numerals, there are a few rules that we need to follow based on the Roman numerals we are trying to write. In this section, we will learn about the rules when writing Roman numerals and how to represent them.

Rule 1: Addition Method:

When a larger symbol is followed by a smaller symbol, we add the numerals to each other. For example, in VI, we have 5 + 1 = 6.

Rule 2: Repetition Method:

A symbol that is repeated up to three times increases the value of the numeral. For example, XXX = 30.

Rule 3: Subtraction Method:

We use the subtraction method when a smaller symbol precedes a larger symbol. For example, XL = 40 (which is 50 – 10).

Rule 4: Limitation Rule:

Symbols cannot be repeated more than three times, and some symbols, such as V, L, and D, cannot be repeated. For example, 10 is represented as X and not VV.

Let us learn about how to write CMXXI in Roman numerals. There are two methods that we can use to write Roman numerals:

• By Expansion Method
• By Grouping Method

The breaking down of Roman numerals into parts and then converting them into numerals is what we call the expansion method. The expansion method involves breaking down Roman numerals into numerical form and adding or subtracting them to get the final number.

Step 1: Break the Roman numerals into parts.

Step 2: Now write each of the Roman numerals with its numerical digit in the place value.

Step 3: Add and subtract the numerals together.

For CMXXI,

Step 1: First, we break the Roman numerals. CMXXI = C + M + X + X + I

Step 2: Write the Roman Numerals for each part.

The Roman Numeral C is 100

The Roman Numeral M is 1000

The Roman Numeral X is 10

The Roman Numeral I is 1

Step 3: Combine all the numbers with subtraction where necessary. C + M + X + X + I = 1000 - 100 + 10 + 10 + 1 = 921.

Therefore, the Roman Numeral CMXXI is 921.

Using subtraction and addition rules, we will apply the grouping method. This means we break the Roman numerals into smaller groups, which makes it easier to work with. This method groups the Roman numerals logically, and then we write the numbers for each group.

Step 1: Take the largest number and write the number for that Roman numeral.

Step 2: Write the Roman numeral using the subtraction and addition rules.

Example: Let’s take the Roman numeral CMXXI.

Step 1: The larger Roman numerals are what we will begin with. Once split, the Roman numerals we get are CM and XXI. The numeral for CM is 900

Step 2: Now we need to either add or subtract the smaller number, depending on its place.

Here we add XXI to CM and we will get CMXXI. The Roman numeral XXI is 21 Therefore, the numeral of CMXXI is 921.

We follow a pattern when it comes to writing Roman numerals. In this section, we will write some numbers related to the Roman numeral CMXXI:

• Limitation Rule: There are some symbols that cannot be repeated more than once (V, L, D). For example, LVV for 60 is wrong, the correct answer is LX.

• Subtraction Rule: This rule is used when a smaller numeral precedes a larger numeral, indicating subtraction. For example, IX is 9.

• Place value: The position of a digit in a number, this position determines its value. For example, the number 2 in 921 is in the hundred's place.

• Grouping Method: A method of breaking down Roman numerals into smaller groups to simplify the addition and subtraction process.

• Prime Number: A number that has only two factors or multiples is called a prime number. For example, 23 is a prime number that has only two factors, 1 and itself.