1. Math 409/409G History of Mathematics Roman Numerals

2. No doubt, you all remember them. They’re displayed at the right. But do you remember how to use them? The Roman numeration system is essentially additive with some subtractive and multiplicative properties thrown in.

3. Examples Additive 11 is 1 after 10 Subtractive 9 is 1 before 10 Multiplicative

4. Roman numeral additive rule If the Roman symbols decrease in value from left to right or the number in our system does not contain 4’s or 9’s, their values are added. Examples:

5. Roman numeral subtractive rule For numbers involving 4’s or 9’s, the letter of the smaller unit is placed before the higher unit. Examples: 4 = 5 – 1 = IV 9 = 10 – 1 = IX 40 = 50 – 10 = XL 90 = 100 – 10 = XC 400 = 500 – 100 = CD 900 = 1000 – 100 = CM

6. The Roman numeral subtractive rule for numbers involving 4’s and 9’s requires that: I comes before only V or X. X comes before only L or C. C comes before only D or M.

7. Examples:

8. Roman numeral multiplicative rule To multiply a Roman numeral by 1000, place a bar on top of it; to multiply it by 1000 2, place a double bar on top. Examples:

9. This ends the lesson on Roman Numerals