Roman numerals

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:

• 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:

• 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)