Roman Numerals
The way we write numbers, using HinduArabic numerals, is hardly the only way to do so. Many
civilizations used other means to denote numbers. For example, the
Romans represented numbers using the numerals I, V, X, L, C, D, and M.
These numerals represent the following numbers:
Roman Numeral 
HinduArabic Equivalent 
I 
1 
V 
5 
X 
10 
L 
50 
C 
100 
D 
500 
M 
100 
There are a few rules for writing numbers with Roman numerals.

Repeating a numeral up to three times represents addition of the number.
For example, III represents 1 + 1 + 1 = 3. Only I, X, C, and M can be
repeated; V, L, and D cannot be, and there is no need to do so.

Writing numerals that decrease from left to right represents addition of
the numbers. For example, LX represents 50 + 10 = 60 and XVI represents
10 + 5 + 1 = 16.

To write a number that otherwise would take repeating of a numeral four
or more times, there is a subtraction rule. Writing a smaller numeral to
the left of a larger numeral represents subtraction. For example, IV
represents 5  1 = 4 and IX represents 10  1 = 9. To avoid ambiguity,
the only pairs of numerals that use this subtraction rule are
Roman Numeral 
HinduArabic Equivalent 
IV 
4 = 5  1 
IX 
9 = 10  1 
XL 
40 = 50  10 
XC 
90 = 100  10 
CD 
400 = 500  100 
CM 
900 = 100  100 

To represent larger numbers, a bar over a numeral means to multiply the
number by 1000. For example, represents
1000 x 500 = 500,000 and
represents 1000 x 1000 = 1,000,000, one million.
Problem 1.
Write the following numbers using Roman Numberals:
 47
 123
 1998
 2345
Problem 2.
Write the following numbers using HinduArabic numerals:
 DCXLVIII
 MMDXLIX
 MCMXLIV
 MCMXCIX
Problem 3.
What is the largest number you can write in Roman numerals without
using bars?
Problem 4.
Perform the following arithmetic operations. Can you
do these without converting the numbers to usual notation?
 LXVI + XXXIV
 CXLVII + MCV
 XXXIV × XLV