Playing with Roman Numerals

In schools and everyday life we are using Arabic numerals, which have 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.  

Ancient Romans used letters from Latin alphabet to write numbers.   There are seven basic letters in Roman numerals: I, V, X, L, C, D, and M.   Each of the letters have certain value and by combining the letters together other numbers are created.

Roman                   Arabic 

I          1

V        5

X        10

L         50

C        100

D        500

M       1,000

How do we create the numbers?

When you write the letters together you add the values, except when the lower value proceeds the higher value. See examples below:

Roman numeral	Equivalent to	Something to keep in mind
I	1	Only I, X, C, and M can be subtracted I can only be subtracted from V or X X can only be subtracted from L or C C can only be subtracted from D or M Never subtract V, L, and D
II	1+1=2
III	1+1+1=3
IV	5-1=4
VI	5+1=6
VII	5+1+1=7
VIII	5+1+1+1=8
IX	10-1=9
XI	10+1=11
XX	10+10=20
XXX	10+10+10=30
Xl	50-10=40
LX	50+10=60
XC	100-10=90
CXX	100+10+10=120
cXL	100+50-10=140
CC	100+100=200
CD	500-100=400
DC	500+100=600
DCC	500+100+100=700
CM	1,000-100=900
MC	1,000+100=1,100

Now the fun begins. Here are some cool examples:

DCCCLXXII

500 + 100 + 100 + 100 + 50 +10 + 10 + 1 + 1 = 872

CMLV

C before M, means 1,000 – 100 = 900,

L = 50

V = 5

900 + 50 + 5 = 955

XCIX 

X before C means 100 – 10 = 90

I before X means 10 – 1 = 9

90 + 9 = 99

How about going the other way:

994 = 900 + 90 + 4

900 = 1,000 – 100, lower value comes before higher: CM

90 = 100 – 10, lower before higher: XC

4 = 5 – 1, lower before higher: IV

CMXCIV

453 = 400 = 50 + 3

400 = 500 – 100, lower before higher: CD

50 = L

3 = III. 

CDLIII

1,640  = 1,000 + 600 + 40

1,000 = M

600 = 500 + 100, means DC

40 = 50 – 10, lower before higher:  XL

MDCXL

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BIBLIOGRAPHY

Adler, David A., Fun With Roman Numerals, Holiday House, New York, 2008.