Roman numerals
Topic Notes
In this lesson, we will learn:
- How to read and write Roman Numerals using addition and subtraction
Notes:
- The numbers we see in math are called Western Arabic numerals (using the digits 0 to 9)
- The ancient Romans used a different set of numeralsRoman Numerals
- There is NO Roman Numeral for zero
- We still see and use Roman Numerals (i.e. naming chemical compounds, royal names, on some clocks and buildings, in laws and contracts)
- Roman Numerals use 7 alphabetic letters as symbols to represent thousands of numbers:
![Representing Numbers: Roman Numerals](
https://dmn92m25mtw4z.cloudfront.net/img_set/math5-2-4-x-1/v1/math5-2-4-x-1-1118w.jpg)
- You can use the mnemonic to help you memorize: IVys XL CD-roMs
- Roman Numerals only represent the digits 1 and 5 (in different place values)
- You read Roman Numerals from left to right and calculate the value by addition or subtraction.
- Use addition if your values are decreasing OR repeating (big to small)
- ex. XXVIII = 10 + 10 + 5 + 1 + 1 + 1 = 28
- REPEATING only happens for symbols that represent a 1 digit (only I, X, C, and M are repeated)
- Symbols can only repeat 3 times maximum (only one exception: 4000 = MMMM)
- Use subtraction if your values are increasing (small to big)
- ex. IV = 1 then 5 is increasing; subtract = (5 1) = 4
- ex. IX = 1 then 10 is increasing; subtract = (10 1) = 9
- Note that Roman Numerals only use subtraction when there is a digit of 4 or 9
- Notice that:
![Representing Numbers: Roman Numerals](
https://dmn92m25mtw4z.cloudfront.net/img_set/math5-2-4-x-2/v1/math5-2-4-x-2-1329w.jpg)
- For 1,2,3 digits: use the same power of ten symbol and repeat them
- For 4 and 9 digits: use subtraction to calculate the value
- For 5 digits: introduces a new symbol
- For 6,7,8 digits: use the power of 5 symbol, then write the power of ten symbol and repeat (just like for 1,2,3 digits)