Roman Numerals look like the English letters I, V, X, L, C, D, and M.
A single "lower" value letter is used before a "higher" value to indicate the number immediately prior to the higher (rather than 4 consecutive identical letters). In this manner, no more than 3 of any letter is required to form any number up to 2999.
Thus one can write the first 11 numbers:-
I = one
II = two
III = three
IV = four
V = five
VI = six
VII = seven
VIII = eight
IX = nine
X = ten
XI = eleven
IXX= nineteen
XX = twenty
XXI = twenty one
L= fifty
LX= sixty
C= one hundred
M= one thousand
MCMLXVII=one thousand nine hundred and sixty seven
MMCM = two thousand nine hundred
etc.
After MMCM =2900, a larger number of M's could be used, or represented by a bar across the top of a letter indicating a factor of 1000.
(i.e. barred V= 5000, barred M= 1,000,000)
For the source and more detailed information concerning this subject, click on the related links section (Wikipedia) indicated below.
The Roman numerals are XLV.
20 in Roman numerals is XX.
Arabic ' 12 Roman ; XII Look ant any classical analogue clock, you will see the '12' written in Roman numerals 'XII'.
MCMLXXXIX
DCLXVI
The Roman numerals are XLV.
18 in roman numerals looks like XVIII
20 in Roman numerals is XX.
300 would be represented by 'CCC' in roman numerals.
Arabic ' 12 Roman ; XII Look ant any classical analogue clock, you will see the '12' written in Roman numerals 'XII'.
MCMLXXXIX
DCLXVI
MCMLII
XXI
XL
MCMLXV
MMI