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Roman Numbers



Explanation
Roman Numbers are one of the oldest system of writing numerals. This system of writing was developed by Roman people around 2000 years ago. Romans used seven letters of alphabets as basic symbols for writing numerals. These seven alphabets are shown in following table :-

Roman alphabetsEquivalent Numeric Value
I1
V5
X10
L50
C100
D500
m1000


Read the following points to be kept in mind while writing numbers in Roman System

1). Alphabets I, X, C and M can be repeated and Repetition means addition.
For example :-
II = 1 + 1 = 2, III = 1 + 1 + 1 = 3
XX = 10 + 10 = 20 , XXX = 10 + 10 + 10 = 30
CC = 100 + 100 = 200, CCC = 100 + 100 + 100 = 300
MM = 1000 + 1000 = 2000, MMM = 1000 + 1000 + 1000 = 3000
Note :- Repetition cannot be more than 3 times. Also Symbols V, L, D cannot be repeated.

2). An alphabet of lesser value written on the left side of an alphabet of greater value is always subtracted from greater value alphabet.
For example :-
IX = 10 - 1 = 9
CM = 1000 - 100 = 900
IV = 5 - 1 = 4

3). An alphabet of lesser value written on the right side of an alphabet of greater value is always added to greater value alphabet.
For example :-
XI = 10 + 1 = 11
VI = 5 + 1 = 6
MC = 1000 + 100 = 1100

4). Following are some more tips on subtraction of Roman Numbers.

(a) Alphabet I can be subtracted from V and x only :-
IV = 5 - 1 = 4
IX = 10 - 1 = 9

(b) Alphabet X can be subtracted from L, M and C only :-
XL = 50 - 10 = 40
XM = 1000 - 10 = 990
XC = 100 - 10 = 90

(c) Alphabet C can be subtracted from D and M only :-
CD = 500 - 100 = 400
CM = 1000 - 100 = 900

(d) Alphabet V,L and D are never subtracted which means that alphabets V, L and D are never written on the left side of greater value alphabet.

(e) When an alphabet of lesser value is placed between two alphabets of greater value, it is always subtracted from alphabet placed on its right side.
For Example :-
VIV = 5 + (5 - 1) = 5 + 4 = 9
XIV = 10 + (5 - 1) = 10 + 4 = 14


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