Roman Numeral number system with examples

Symbol values

I    1
            _
V    5      V     5,000
            _
X   10      X    10,000
            _
L   50      L    50,000
            _
C  100      C   100,000
            _
D  500      D   500,000
            _
M 1000      M 1,000,000

Decimal to Roman Numeral
                         
                           year
                           1777  MDCCLXXVII
                           1888  MDCCCLXXXVIII
                           1999  MCMXCIX  or MIM
             50  L         2000  MM
1  I         51  LI        2001  MMI
2  II        52  LII       2002  MMII
3  III       53  LIII      2003  MMIII
4  IV        54  LIV       2004  MMIV
5  V         55  LV        2005  MMV
6  VI        56  LVI       2006  MMVI
7  VII       57  LVII      2007  MMVII
8  VIII      58  LVIII     2008  MMVIII
9  IX        59  LIX       2009  MMIX
10 X         60  LX        2010  MMX

20  XX      200  CC        2015  MMXV
30  XXX     300  CCC       2016  MMXVI
40  XL      400  CD        2017  MMXVII
50  L       500  D         2018  MMXVIII
60  LX      600  DC        2019  MMXIX
70  LXX     700  DCC       2020  MMXX
80  LXXX    800  DCCC      2030  MMXXX
90  XC      900  CM        2040  MMXL
99  XCIX or IC 
100 C  

General rules for forming a Roman Numeral.
No more than three of any symbol together.
To add all: largest to smallest symbol.
To subtract:  smaller precedes larger symbol
              typical is symbol 1 or 2 smaller
              4  IV
              9  IX
             40  XL
             90  XC
            400  CD
            900  CM
Multiple subtractions keep larger symbol preceding smaller larger symbol
             99  XCIX    or  IC
            999  CMXCIX  or  IM
                  _             _
           9999  MXCMXCIX  or  IX

I do not have the elementary school rules for add, subtract, multiply, divide 
I would expect: add from smallest to largest, rewriting as you proceed.

Last updated 10/28/2019