Gray Morris

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Unit One: Chapter 1

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After reviewing this chapter, you should be able to:

› Recognize the symbols used to represent numbers in the Roman numeral system

› Convert Roman numerals to Arabic numbers

› Convert Arabic numbers to Roman numerals

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History Application in apothecary system

› Grains (gr) combined with Roman numerals› x = 10 in Roman numeral expressions

Note: “gr” precedes the number in Apothecary system

x 10 gr grains

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Roman numerals and time pieces

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May still see in practice› Aspirin gr x = Aspirin 10 grains

Knowing values helps prevent errors

Safety Tip The Institute for Safe Medication Practice (ISMP) at www.ismp.org

› Recommendation: abbreviations and med errors

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Arabic system—numbers› Numbers not letters (1, 2, 3…)› Fractions (¼, ¾)› Decimals (0.5, 1.2)

Roman Numerals—letters› i, v, x used most often› Line may be used to prevent

interpretation error

i, vii, ix

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1. When a Roman numeral of lesser value is placed AFTER one of equal value, the numerals are added25 = xxv (x = 10 x = 10 , v = 5 10+10+5

= 25)

2. Same numeral is never repeated more than three times

4 = iv NOT iiii

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3. When a Roman numeral of lesser value is placed BEFORE a numeral of greater value, the numbers are subtracted

ix = 9 (x = 10, i = 1 10 - 1 = 9)

xxiv = 24 (x = 10 + x = 10 + iv = [5 – 1] = 24)