roman numbers
DESCRIPTION
Grade 6 presentation on Roman NumeralsTRANSCRIPT
Roman NumeralsAn Introduction
Why Roman NumbersO 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
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:
The Roman NumeralsO Large numbers were written by putting a bar
over the symbol (or set of symbols) to make the number 1000 times larger. Examples:O indicates 5,000 O indicates 6,000O indicates 50,000 O indicates 50,000
O Our lesson will not deal with symbols with bars over them (i.e., all numbers in our lesson will be smaller than 5,000).
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.
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.
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.
Example 1O 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.
Example 2O 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.
Time to PracticeO Use the interactives below to practice
converting from Roman numerals and to Roman Numerals.