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Last updated on March 29th, 2025

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CM in Roman Numerals

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Intermediate
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To meet their daily commerce and administration needs, the ancient Romans developed Roman Numerals. It used a combination of seven symbols — I, V, X, L, C, D, and M to represent numbers. Roman numerals were used to record transactions, keep track of data, and label military units. In this topic, we are going to learn about the Roman numeral CM.

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What is CM 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. CM in Roman numerals can be written in number form by applying the subtraction rule, i.e., CM = 900.

 

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

 

cm roman numerals

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Basic Rules for CM in Roman Numerals

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 VIII, we have 5 + 3 = 8.

 

Rule 2: Repetition Method:

 

A symbol that is repeated three times in continuation 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 more than once. For example, 10 is represented as X and not VV.

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How to Write CM in Roman Numerals?

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

 

  • By Expansion Method
     
  • By Grouping Method
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CM in Roman Numeral by Expansion 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 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: Subtract the numerals as required.

 

For CM,

 

Step 1: First, we break the Roman numerals. CM = C + M

 

Step 2: Write the Roman Numerals for each part

The Roman Numeral C is 100

The Roman Numeral M is 1000

 

Step 3: Apply the subtraction rule M - C = 1000 - 100 = 900.

 

Therefore, the Roman Numeral CM is 900.

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CM in Roman Numeral by Grouping Method

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 CM.

 

Step 1: The larger Roman numerals are what we will begin with. Once split, the Roman numerals we get are C and M. The numeral for M is 1000.

 

Step 2: Now we need to subtract the smaller number, depending on its place. Here we subtract C from M to get CM. The Roman numeral C is 100.

 

Therefore, the numeral of CM is 900.

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Common Mistakes and How to Avoid Them in CM Roman Numerals

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CM Roman Numerals Examples

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Problem 1

How do you express 900 in Roman numerals, and what does it signify in terms of Roman numeral conventions?

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Explanation

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Problem 2

If you subtract DL from MCM, what is the result written in Roman numerals?

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Explanation

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Problem 3

How would you express the product of CM and III in Roman numerals?

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Explanation

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Problem 4

Divide MCM by III. What is the quotient in Roman numerals?

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Explanation

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Problem 5

Convert CM into its decimal form.

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Explanation

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FAQs on CM in Roman Numerals

1.What is D in Roman numerals?

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2.Is CM a prime number?

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3.What is CM + CM?

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4.What is MC?

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5.Subtract C from CM

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Important Glossaries for CM in Roman Numerals

  • Limitation Rule: There are some symbols that cannot be repeated more than once (V, L, D). For example, VV for 10 is wrong; the correct answer is X.

 

  • Place Value: The position of a digit in a number, this position determines its value. For example, the number 9 in 900 is at the hundred's place.

 

  • Subtraction Method: A rule where a smaller numeral is placed before a larger numeral to indicate subtraction. For example, CM is 900.

 

  • Addition Method: A rule where numerals are added to each other when a larger symbol precedes a smaller one. For example, VI is 6.

 

  • Roman Numerals: An ancient numeric system using combinations of letters from the Latin alphabet (I, V, X, L, C, D, M) to represent numbers.
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Hiralee Lalitkumar Makwana

About the Author

Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.

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: She loves to read number jokes and games.

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