Roman numbers

Grade 6 presentation on Roman Numerals

1. Roman Numerals An Introduction

2. Why Roman Numbers Comparing and contrasting our number system * with another helps us recognize and appreciate the richness and power of our number system. Converting between the two offers great practice in computing and pattern recognition. * Our number system is called the Hindu-Arabic System

3. The Roman Numerals Roman Number Hindu-Arabic Number I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numbers are made using the seven symbols as shown below :

4. The Roman Numerals Large numbers were written by putting a bar over the symbol (or set of symbols) to make the number 1000 times larger. Examples: indicates 5,000 indicates 6,000 indicates 50,000 indicates 50,000 Our lesson will not deal with symbols with bars over them (i.e., all numbers in our lesson will be smaller than 5,000).  

5. Writing a Roman Numeral Roman numbers are written by combining a subset of the seven numbers listed in the table. Examples: VII is 5 + 1 + 1 = 7. XIII is 10 + 1 + 1 + 1 = 13 . If a smaller number comes before a larger number, you subtract the smaller from the larger. Examples: IV is 5 ̶ 1 = 4. IX is 10 ̶ 1 = 9.

6. Writing a Roman Numeral Only one digit is subtracted at one time. So, you can't represent 8 as IIX because that's subtracting one from ten twice. Rather, you'd write VIII . XLIV is considered adding (50 ̶ 10) to (5 ̶ 1), or 44, so that's okay. Examples: CIV is 100 + (5 ̶ 1) = 94. LIX is 50 + (10-1) = 59 . The V is never subtracted. The number 45 is written as XLV , not VL .

7. Writing a Roman Numeral A number cannot be subtracted from another number that is ten (or more) times larger. So, I can't be subtracted from L ; V can't be subtracted from C ; and so forth. You'd never write 99 as CIC ; it would be XCIX .

8. Example 1 What is the value of CDXLVI ? C is 100 and D is 500. Since C is smaller than D, we subtract 100 from 500: 400. X is 10 and L is 50. Since X is smaller than L , we subtract 10 from 50: 40. V is 5 and I is 1. Since V is larger than I , we add 5 and 1: 6. Putting it all together, we get 400+40+6 = 446.

9. Example 2 How would you write 2346 as a Roman numeral? M is one-thousand so MM represents two-thousand. C is one-hundred so CCC represents three-hundred. L is fifty and X is ten so XL represents forty. V is five and I is one so VI represents six. Putting it all together, we get MMCCCXLVI .

10. Time to Practice Use the interactives below to practice converting from Roman numerals and to Roman Numerals.