Answer:
add the values of the symbols or symbol pairs
Explanation:
You want to know how to convert Roman Numerals to decimal numbers.
Characters and values
The symbols used in Roman Numerals are {I, V, X, L, C, D, M}. Respectively, they have values {1, 5, 10, 50, 100, 500, 1000}. The values of these symbols are multiplied by 1000 by an overline.
Conversion
A number can be converted to decimal by working right to left. In general, the value of a symbol is added to the total. When a symbol of lesser value than the previous one is encountered, its value is subtracted. (Usually, the value being subtracted is a power of 10.)
Examples
- I = 1
- II = 1 + 1 = 2
- IV = 5 - 1 = 4
- V = 5
- IX = 10 -1 = 9
- MCMLXIX = 10 -1 +10 +50 +1000 -100 +1000 = 1969
Aliases exist. Without knowledge of the rules the Romans used for writing their numbers, we can invent numbers that can be written two or more ways:
1950 = MLM = MCML
As we noted above, the form MLM = 1950 would probably not be used, since the subtracted L is not a power of 10.
We expect that 1999 would likely be written MCMXCIX, rather than MIM. That way, the character being subtracted is not less than 10% of the character it is subtracted from.
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Additional comment
Use of an overline is not the only way that the system is extended to higher values. Different notations are found in different contexts.
The basic idea of Roman Numerals is to express value by the character used, rather than its location in a number. It is not a "place value" system.
There is no zero. There are no negative numbers.
The reference to "symbol pairs" in the Answer section above is to recognize a pair of symbols in which the one on the left is subtracted.