Differences between Roman and Hindu-Arabic systems

The main differences between Roman and Hindu-Arabic numerals are that the Romans did not have a symbol for zero, and the placement of numerals within a number can sometimes indicate subtraction rather than addition. In the Hindu-Arabic number system, each digit in a number has a place value. Take a quick look at what Roman and Hindu-Arabic numerals look like:

Roman numerals
 
Roman Numerals
I = 1
C = 100
V = 5
D = 500
X = 10
M = 1000
L = 50
 
 
Roman Numerals Table
1
I
14
XIV
27
XXVII
150
CL
2
II
15
XV
28
XXVIII
200
CC
3
III
16
XVI
29
XXIX
300
CCC
4
IV
17
XVII
30
XXX
400
CD
5
V
18
XVIII
31
XXXI
500
D
6
VI
19
XIX
40
XL
600
DC
7
VII
20
XX
50
L
700
DCC
8
VIII
21
XXI
60
LX
800
DCCC
9
IX
22
XXII
70
LXX
900
CM
10
X
23
XXIII
80
LXXX
1000
M
11
XI
24
XXIV
90
XC
1600
MDC
12
XII
25
XXV
100
C
1700
MDCC
13
XIII
26
XXVI
101
CI
1900
MCM
 
 
Hindu-Arabic numerals
 
Arabic or Hindu numerals or Hindu-Arabic numerals are the ten numerical digits we are familiar with modern numbers.
 
Hindu-Arabic Numerals
0
1
2
3
4
5
6
7
8
9
 
A sequence of numerals such as “13” or “768” is read as a whole number.
 
In Roman numerals, when a smaller number is in front of a larger one, it is subtracted from the larger number. When a smaller number is after the larger one, it is added to the larger number.

Example:

Placing I in front of the V, or placing any smaller number in front of any larger number, indicates subtraction. So IV means to subtract I from V, which leaves 4, and IX means to subtract I from X, which leaves 9.

Placing I after the V means addition, so VI means 6, VII means 7, VIII means 8.

Place value

Roman numerals can be changed into Hindu-Arabic numbers by taking the place value columns (highest lowest) of the Hindu-Arabic number and gradually building up the Roman numeral.

Example:

The Roman numeral for 2 305 is MMCCCV.

Example:

99 = 90 + 9
or XC + IX XCIX

So, XCIX is the Roman numeral for 99.
(Note: It is usually not represented by IC.)