CDXX Roman Numerals: Rules, Solved Examples and Practice Questions

CDXX Roman numeral represents the number 420. Roman numerals were used in ancient Rome and are still commonly seen today on clocks, books, monuments, and historical records. To convert 420 into Roman numerals, we break it down using the values of each Roman symbol: 400 + 20 = 420. Using Roman symbols, 400 is CD (500 - 100), and 20 is XX (10 + 10). Therefore, 420 is written as CDXX. Learning to read and write numbers like CDXX helps students understand number patterns and develop logical thinking by combining values step by step.

Table of Contents

• How to Write CDXX Roman Numeral in Numbers?
• Numbers Related to CDXX Roman Numerals
• Basic Rules for Writing Roman Numerals
• Solved Examples on CDXX Roman Numeral
• Practice Questions on CDXX Roman Numeral
• Conclusion

 

How to Write CDXX Roman Numeral in Numbers?

Roman numerals can be converted to numbers by understanding the value of each symbol and following the basic rules of addition and subtraction.

In CDXX, the letters represent the following values:

• C = 100

• D = 500

• X = 10

The Roman numeral CDXX uses the subtraction rule, where C comes before D, meaning 100 is subtracted from 500. Then, we add the values of the two X symbols.

Step by step:

• D - C = 500 - 100 = 400

• X + X = 10 + 10 = 20

Now, add the two results together:

• 400 + 20 = 420

• Therefore, CDXX = 420 in numbers.

 

Numbers Related to CDXX Roman Numerals

Basic Rules for Writing Roman Numerals

Roman numerals follow specific rules for correct representation:

• Repeat rule: A symbol (such as I, X, C, or M) can be repeated up to three times. Example: XXX = 30

• Subtraction rule: When a smaller numeral comes before a larger number, subtract it. Example: CD = 400

• Addition rule: When a smaller numeral comes after a larger one, you add it. Example: XX = 20

• No repetition rule: V, L, and D cannot be repeated.

 

Solved Examples on CDXX Roman Numeral

Example 1: Find the value of CDXX in numbers.

Solution:

• CD = 400

• XX = 20

• Add them: 400 + 20 = 420

Example 2: Write 420 in Roman numerals.

Solution:

• 400 = CD

• 20 = XX

Combine them CDXX.

Example 3: Express 400 and 420 in Roman numerals.

Solution:

• 400 = CD

• 420 = CDXX

So, CDXX is 20 more than CD.

Example 4: Identify the Roman numeral before and after CDXX.

Solution:

• Before: CDXV = 415

• After: CDXXV = 425

Example 5: What is the sum of CDXX (420) and XXX (30) in Roman numerals?

Solution:

• CDXX = 420

• XXX = 30

Total = 450 = CDL

Practice Questions on CDXX Roman Numeral

1. Write CDXX in expanded form using addition and subtraction.
2. Convert 420 into Roman numerals.
3. Find the sum: CDXX + L (write the answer in Roman numerals).
4. Find the difference: CDXX − XX (write the answer in Roman numerals).
5. Multiply CDXX by II and write the answer in Roman numerals.
6. Divide CDXX by X and write the answer in Roman numerals.
7. Which is greater: CDXX or CDXXX?
8. Arrange in ascending order: CDX, CDXX, CDXL.
9. What number must be added to CDXX to get D? Write the answer in Roman numerals.
10. A warehouse stores CDXX items. If L items are removed, how many remain? Write in Roman numerals.
    
    

Conclusion

CDXX Roman numerals equal 420. It combines CD (400) using the subtraction rule and XX (20) using the addition rule. This numeral illustrates how the Roman system constructs numbers by combining subtraction and addition principles. Roman numerals like CDXX are still commonly seen in historical inscriptions, clocks, monuments, and book chapters. Understanding CDXX and similar numerals helps students strengthen their knowledge of number systems and develop logical thinking.

Learn CDXX Roman numerals in a clear and structured way at Orchids International School.