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What is the Difference between Additive notation and Subtractive notation in Roman numerals?

correct me if im wrong but this is an example of Additive: XXXIII = 10 + 10 + 10 + 1 + 1 + 1 = 33

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    Yes, that’s an example of additive notation. IX $=10-1=9$ is an example of subtractive notation, as is XC $=100-10=90$. Roman numerals were originally entirely additive; the subtractive notation was a later development.2012-05-23
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    Thanks for that you made it really clear :)2012-05-23
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    @BrianM.Scott what would you say is the subtractive notation of my example though?2012-05-23
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    There isn’t one: the subtractive notation is used only when an amount written with a single letter is being subtracted. One doesn’t write IIV, meaning $5-2$, for $3$, and similarly, one doesn’t write XXXIIV, XXLIII, or XXLIIV, meaning $30+5-2,50-20+3$, and $50-20+5-2$, for $33$.2012-05-23
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    I see thanks alot :)2012-05-23
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    In fact, `IIII` was used for 4; some clocks still use it. As I heard it, Julius Caesar objected and introduced the reform of writing it as `IV` because `IIII` looked too similar to the beginning of `IULIUS`.2012-05-23
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    Just as an example for subtractive notation, 1999 is not generally written "IM", as might be supposed, but rather "MCMXCIX".2012-07-02
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    See http://groups.google.com/group/sci.math/browse_thread/thread/590a24a7df8a670f2012-07-02

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IIII and IV are both used for 4. IIII is additive; IV is subtractive.

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    Actually four repetitions of the same symbol became common during the Middle Ages. During the golden age of the Roman civilization (I century BC) only up to three repetitions were allowed by "proper grammar", so to speak.2012-07-02
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    @Andy This seems to be the opposite of what Wikipedia claims: https://en.wikipedia.org/wiki/Subtractive_notation2017-12-26