﻿ MA Pharm.com: Pharmacology Review for Medical Assistants - Roman Numerals on a Prescription Form | Write Roman Numbers
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The main differences between Roman and Arabic numerals are that Roman numerals lack a symbol for zero, and that numeral placement within a number can sometimes indicate subtraction rather than addition. In order to write, read, and fill out prescriptions the healthcare professional must understand Roman numerals. Roman numerals are commonly used in pharmacology, especially when it comes to the Sig on prescriptions. For example:

Take three tablets three times a day is often written as III tabs t.i.d.

 I The easiest way to write a roman number is to mark that many lines down - they look like little i's. Thus I means 1, II means 2, III means 3. However, four strokes seemed like too many.... V So the Romans moved on to the symbol for 5 - V. PlacingI in front of the V — or placing any smaller number in front of any larger number — indicates subtraction. So I before V as inIV means 4. After V comes a series of additions - VI means 6, VII means 7, VIII means 8. X X means 10. But what about 9? Same thing. IX means to subtract I from X, leaving 9. Numbers in the teens, twenties and thirties follow the same rule as the first set, only with X's indicating the number of tens. So XXXI is 31, and XXIV is 24. L L means 50. Based on what you've learned, I bet you can figure out what 40 is. You guessed it right, that's XL, since 10 subtracted from 50 is 40. And thus 60, 70, and 80 are LX, LXX and LXXX. C C stands for centum, the Latin word for 100. A century lasts 100 years. We still use this word in "cent" (one hundredth of a dollar) and centimeter (one hundredth of a meter). The subtraction rule means 90 is written as XC. Like the X's and L's, the C's are tacked on to the beginning of numbers to indicate how many hundreds there are: CCCLXIX is 369. D D stands for 500. As you can probably guess by this time, CD means 400. So CDXLVIII is 448. (See why we switched systems?) M M is 1,000. You see a lot of Ms because Roman numerals are used a lot to indicate dates. For instance, if you know someone that was born in 1998 then that year is written as MCMXCVIII. V Larger numbers were indicated by putting a horizontal line over them, which meant to multiply the number by 1,000. Hence the V on the has a line over the top, which means 5,000. This usage is no longer current, because the largest numbers usually expressed in the Roman system are dates, as discussed above.

* adapted from Nova Roma on Roman Numerals under Fair Use

## Roman Numeral to Arabic Numbers

 I = 1 II = 2 III = 3 IV = 4 V = 5 VI = 6 VII = 7 VIII = 8 IX = 9 X = 10 XX = 20 XXX = 30 XL = 40 L = 50 LX = 60 LXX = 70 LXXX = 80 XC = 90 C = 100 CC = 200 CCC = 300 CCCC = 400 D = 500 DC = 600 DCC = 700 DCCC = 800 CM = 900 M = 1,000 MM = 2,000 MMM = 3,000 MMMM = 4,000 V = 5,000 VM = 6,000 VMM = 7,000 VMMM = 8,000 MX = 9,000 X = 10,000 XX = 20,000 XXX = 30,000 XXXX = 40,000 L = 50,000 LX = 60,000 LXX = 70,000 LXXX = 80,000 XC = 90,000 C = 100,000 CC = 200,000 CCC = 300,000 CCCC = 400,000 D = 500,000 DC = 600,000 DCC = 700,000 DCCC = 800,000 CM = 900,000 M = 1,000,000 Take the Roman Numeral Challenge at Fact Monster  Subject Navigation:          Self-Study Navigation      