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### Roman Numerals

```
Date: 01/13/97 at 11:34:45
From: Robert
Subject: MCMLXXXVI

I am trying to learn how to read Roman Numerals.
What does MCMLXXXVI mean?

Robert
```

```
Date: 01/13/97 at 12:35:12
From: Doctor Rob
Subject: Re: MCMLXXXVI

Dear Robert -

First you need to know the values of the letters, and then you need to
know what the positions of the letters mean.

Values:

I  1
V  5
X  10
L  50
C  100
D  500
M  1000
_
V  5000

When a letter is repeated one, two, or three times, add up the value
that many times.  XXX = 10 + 10 + 10 = 30.  MM = 2000.

V, L, and D cannot be repeated.
I, X, C, and M can be repeated up to 3 times.

If you want to repeat a letter 4 times, instead use that letter
preceding one of the two next larger values:

For 4, don't use IIII, but instead IV
(I subtracted from V).
For 9, don't use VIIII or VIV, but instead IX
(I subtracted from X).

Similar rules apply for 40, 90, 400, 900. Write the resulting groups
in descending order.

794 = 500 + 200 + 90 + 4
= D + CC + XC + IV
= DCCXCIV

Note that this only works up to 3999.  For larger numbers, more
letters would have to be assigned the values of 5000, 10000, and
so on.

To read a numeral, reverse this process.  Start at the left, and
read off groups which either consist of repetitions of a single
letter, or one of the groups IV, IX, XL, XC, CD, CM (representing
4, 9, 40, 90, 400, or 900, respectively).  You can recognize when
these groups occur because the letters are not in descending order.
Add up the values of those groups.

MCMLXXXVI = M + CM + L + XXX + V + I
= 1000 + 900 + 50 + 30 + 5 + 1
= 1986

I hope this helps.

-Doctor Rob,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
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