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Roman numerals read like English writing and the numbers we use in America and most other countries. However, Roman numerals require some simple rules to be followed so that they can be written correctly. Below are the rules for Roman numerals. Read them to your students and help them understand how these rules apply by giving them the demonstration that follows each rule in this section.
- Only one smaller digit can be on the left side of the larger digit. For example, the number 7 would be written as "VII" rather than "IIIX".
- If the digit to the left represents a smaller amount than the digit to the right, it is to be subtracted from the digit on the right. For example "IV" means 4.
- If the digit to the right is smaller than the digit on the left, the numbers shall be added together. For example "VI" means 6.
- The smaller digit on the left can be no less than 10% of the digit on the right. For example, "IM" is not a "legal" form of 999. It would instead be written as "CMXCIX".
- The least amount of digits must be used without breaking any of the other rules. For example, thought XXXX can mean "50", you would instead use the "L".
Use the section below to help your students come one step closer to learning how to read Roman numerals.
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How to Read Roman Numerals Review Activity
- Write the following Roman numerals on the board and ask students to tell you if this is the correct way for them to be written.
- Walk through the rules for each number.
- Ask students to look at the number and review the rules to decide if the answer is correct. For instance, if the number is IIX, you would first ask the students to look at rule #1, which demands that there be only one smaller digit to the left of the larger digit.
- Ask students to change the way the number is written so that it follows rule #1. Students should change it to "VIII".
- Move on to rule #2 There are no smaller digits to the left anymore.
- Rule #3 is used to add the V+I+I.
- Rule #4 is not considered because the answer has been changed so that no smaller digit is on the left.
- A look at rule #5 reminds you to review so that the smallest amounts of digits are used without breaking any of the other rules.
- Repeat this procedure for converting Roman numerals on the list below.
- VV (This should actually be written as X)
- IIL (This should actually be written as XLVIII )
- CM (This correctly represents 900)
- CCM (This should be written as DCCC)
- LL (This should be written as C)
Review the information that you have given the students in this lesson plan. Make sure that they understand the rules of Roman numerals before moving on to the next lesson plan that teaches them more about how to read Roman numerals.