Before students begin this lesson, they should be taught the rules of Roman numerals as instructed in the previous lesson plan. Once the students understand which each Roman numerals means and understands the rules that accompany them, explain the method below to your students. Then they too can begin converting Roman numerals to standard numbers.
Reading and writing Roman numerals means understanding what each symbol represents as well as what math function should be performed. Look at the Roman numeral below.
When you look at this number, the first thing to look for is to see if there are any digits representing smaller digits on the left side of the larger digits. The answer to this question will tell you what math function to perform. In this case, the digits descend from highest to lowest where M=1000, D=500, C=100, X=10, V=5 and I=1. This tells you that you will add the numbers together, which is something you will do as the last step in deciphering every Roman numeral. The number is 1616 by the formula of 1000+500+100+10+5+1
Have students practice using the following numbers.
- CVII (107)
- MDX (1510)
- MC (1100)
Sometimes you will have to subtract before you can add when converting Roman numerals to standard numbers. Use the number below as an example.
There is a C before the M, an X before the C and a I before the V. Before taking the last step in converting the Roman numerals by adding them, you must first subtract the smaller numbers on the left from the larger ones on the right. The formula for figuring out this Roman numeral would look like this; 1000 + (1000-100) + (100- 10) + (5-1) because the way the Roman numeral is written is actually the formula listed after this sentence. M + (M-C) + (C-X) + (V-I) We simply translated it! The answer to the formula is 1994.
Have the students convert the Roman numerals below.
- MM (2000)
- MCMVI (1906)
- XXIII (23)
- LVI (56)
- DIII (503)
- MCDIV (1404)
Now that students have learned about converting Roman numerals to standard numbers, they are ready to move on to the next lesson plan in this series which will teach them how to write Roman numerals.