NCERT Class 6 Math Roman Numerals

Romans represented numbers using the numerals I, V, X, L, C, D, and M only.

Roman Numerals

The table below shows Hindu - Arabic equivalent of I, V, X, L, C, D, and M

Roman Numeral	Hindu-Arabic Equivalent
I	1
V	5
X	10
L	50
C	100
D	500
M	1000

The rules to be followed for writing numbers with Roman numerals are as follows-

• Repeating a numeral in succession represents addition. For example, II = 1+1 = 2. Similarly, III = 1+1+1 = 3. Also, CCC = 300
• A numeral can be repeated in succession up to three times only. For example, 4 cannot be written as IIII.

• V (5), L (50), and D (500) cannot be repeated. For example, you cant write 10 as VV. 

• When a numeral of lower value is written to the right side of numeral of higher value, the values of all the digits are added. For instance, VI = 5 +1 =6. and XVI = 10 + 5 + 1 = 16.
• When a numeral of lower value is written to the left side of numeral of higher value, it represents subtraction. For instance, IV = 5 - 1 = 4. This rule is used to write a number that otherwise would take repeating of a numeral four or more than four times. Writing a smaller numeral to the left of a larger numeral represents subtraction. For example, IX = 10 - 1 = 9. VIIII cannot be used to represent 9 since a numeral can be repeated in succession up to three times only. Only pairs of numerals that use this subtraction rule are

• Roman Numeral	Hindu-Arabic Equivalent
  IV	4 = 5 - 1
  IX	9 = 10 - 1
  XL	40 = 50 - 10
  XC	90 = 100 - 10
  CD	400 = 500 - 100
  CM	900 = 1000 - 100

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• A bar over a numeral means to multiply the number by 1000. For example, V = 15 and M = 1000, but
• 
                    
• The symbols V, L and D are never written to the left of a symbol of greater value, i.e. V (50), L (50) and D (500) are never subtracted.
• The symbol I (1) can be subtracted from V (5) and X (10) only.
• The symbol X (10) can be subtracted from L (50), M (1000) and C (100) only.

Also Refer - Knowing Your Numbers (Class 6)