Roman Numerals

Roman numerals are used in Pharmacy by practitioners on prescription drug orders and on packaging to designate DEA schedules for controlled substances. 

The Basics
A smaller number in front of a larger number means subtraction, all else means addition. For example, IV means 4, VI means 6.

You would not put more than one smaller number in front of a larger number to subtract. For example, IIV would not mean 3.

You must separate ones, tens, hundreds, and thousands as separate items. That means that 99 is XCIX, 90 + 9, but never should be written as IC. Similarly, 999 cannot be IM and 1999 cannot be MIM.

Sometimes you will see a numeral with a line over it. That means to multiply it by 1000. A numeral V with a line over it means 5000. This usage is no longer current, because the largest numbers usually expressed in the Roman system are dates.

Symbols
I	The numeral one. II is two, III is three. You seldom see IIII as 4, since IV can also mean 4, plus its shorter to write.
V	The numeral 5. IV is 4, VI is 6, VII is 7, VIII is 8.
X	The numeral 10. IX is 9, XI is 11, etc.
L	The numeral 50. XL would be 40.
C	The numeral 100. Think of Century having a hundred years. C is short for the Latin word Centum, but that's not very easy to remember.
D	The numeral 500.
M	The numeral 1000.

Roman Numerals Chart 1-100
1	I
2	II
3	III
4	IV
5	V
6	VI
7	VII
8	VIII
9	IX
10	X
15	XV
20	XX
25	XXV
30	XXX
35	XXXV
40	XL
45	XLV
50	L
55	LV
60	LX
65	LXV
70	LXX
75	LXXV
80	LXXX
85	LXXXV
90	XC
95	XCV
100	C