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What is the Roman numeral system?

Clock in Bad Salzdetfurth, Germany, Badenburger Strasse

Clock in Bad Salzdetfurth, Germany, Badenburger Strasse

Roman numeral system, a way of representing numbers by letters of the Roman alphabet. In the system the letters I, V, X, L, C, D, and M stand for 1, 5, 10, 50, 100, 500, and 1,000, respectively. Other numbers are formed by arranging these seven symbols according to a set of established rules of addition and subtraction.

For example, the number 1,648 would be written in the Roman numeral system as MDCXLVIII. The rules used in arranging the symbols are the following.

If a symbol appears to the right of one of greater or equal value, it is added to it. In the example, VIII means that three l's are added to 5 to yield 8. If a symbol appears to the left of one of greater value, it is subtracted from it. In the example, XL means 10 is subtracted from 50 to yield 40. If a symbol appears between two others of greater value, it is subtracted from the second and the result is added to the first. In the example, XL (40) is added to C (100) , because the symbols appear in the order CXL. Thus, the complete number is read as 1,000 (M), 600 (D+C), 40 (X subtracted from L) , and 8 (V+I+I+I).

It is not known when this way of writing numerals was first used in Rome or exactly how it developed, but because the Roman Empire controlled a great part of Europe for a long time, the use of Roman numerals became very widespread. However, the only mathematical operations that can be performed easily with this system are addition and subtraction. It is also very cumbersome to write large numbers using Roman numerals. The system, therefore, cannot meet the commercial and scientific needs of modern society and, over the past 500 years or so, has become generally obsolete. Roman numerals are now used mainly for ceremonial purposes.

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