I for 1
V for 5
X for 10
L for 50
C for 100
D for 500
And ‘M’ for 1000
If we place a smaller representative of any symbol before the larger symbol, it means that the smaller number is to be subtracted from the larger. On another hand, if we place the smaller symbol after the larger symbol, it indicates that we will add the two symbols.
Let us learn with the following examples: to convert the following Roman Numbers to their decimal form.
XXI – Here we find 'x' appearing twice followed by a symbol 'I', which represents a number 1. So we will add the digits 10 + 10 + 1 = 21.
On another hand if we have the roman number IX, here I is placed before X, so we need to subtract 1 from the number 10 and the decimal numeral so formed will be 10 – 1 = 9.
In the same way if we write XIV, here ‘I’ is placed after 10, but it is placed before 5, so we will write the decimal number as 10 + 5 – 1 = 14.
In another situation, if we have the Roman numeral as XVII, in this case, we observe that the symbol of 5 is smaller than 10 and the symbol 1 is smaller than 5, so it becomes : 10+ 5 + 1 + 1 = 17.