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# Roman numbers

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Grade 6 presentation on Roman Numerals

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### Roman numbers

1. 1. Roman Numerals An Introduction
2. 2. Why Roman Numbers O Comparing and contrasting our number system* with another helps us recognize and appreciate the richness and power of our number system. O Converting between the two offers great practice in computing and pattern recognition. * Our number system is called the Hindu-Arabic System
3. 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. 4. The Roman Numerals O
5. 5. Writing a Roman Numeral O 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. O 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. 6. Writing a Roman Numeral O 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. O The V is never subtracted. The number 45 is written as XLV, not VL.
7. 7. Writing a Roman Numeral O 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. 8. Example 1 O 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. 9. Example 2 O How would you write 2346 as a Roman numeral? O M is one-thousand so MM represents two- thousand. O C is one-hundred so CCC represents three- hundred. O L is fifty and X is ten so XL represents forty. O V is five and I is one so VI represents six. O Putting it all together, we get MMCCCXLVI.
10. 10. Time to Practice O Use the interactives below to practice converting from Roman numerals and to Roman Numerals.