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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
An accurate and easy-to-read resource for students in medical dosage calculation classes
Medical Dosage Calculations For Dummies, 2nd Edition is an accurate guide to dosage calculation that tracks to standard course curricula. It's an easy-to-follow supplementary resource for students of nursing, pharmacology, paramedic programs and beyond, walking you through ratio-proportion, formula, and dimensional analyses for a wide variety of medication types.
You'll learn how medications are given, to whom, and how to chart accurately and clearly. You'll also discover how to handle the processes and language of medical dosing, as well as how to navigate the electronic medical records (EMRs) and electronic health records (EHRs).
Inside:
- Brush up on your math
- Understand the best practices in medical administration, including needle insertion instructions
- Discover evidence-based practice guidelines and methods
Perfect for students currently taking a medical dosage calculations class, Medical Dosage Calculations For Dummies is also a great resource for working professionals interested in brushing up on the fundamentals.
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Veröffentlichungsjahr: 2025
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Medical Dosage Calculations For Dummies®
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: Getting Up to Speed: Reviewing Math Basics
Chapter 1: Brushing Up on Your Math Skills and Entering the Healthcare Field
Knowing What Math You Need to Know in Healthcare
Tools of the Trade for Dosing Meds
Surveying Healthcare Careers (They All Use Medical Math!)
Beyond the Math: Remembering the Human Side of Healthcare
Chapter 2: Using Numbers and Arithmetic
Healthy Numbers: Surveying the Numeral Systems Used in Healthcare
Ingesting a Dose of Numbers
Using Addition to Make Everything Add Up
Seeing Subtraction in Action
Managing Multiplication
Doing Division: Divided We Stand
Real-Life Practice: The RN and the Meds
Real-Life Practice: A Fluid Approach to Fluids
Real-Life Practice: Liquid Assets
Chapter 3: Getting Familiar with Fractions
Using Fractions to Probe between Integers
Conquering Fraction-Related Conversions
Playing the Percentages
Real-Life Practice: Chow Down to Heal Up
Real-Life Practice: Measuring the Mass
Chapter 4: Getting Familiar with Systems of Measurement and Unit Conversions
Looking at the Main Measurement Systems Used in Medicine
Examining the Rules of Conversion
Converting Units in Different Measurement Systems
Real-Life Practice: Filling Up on Fluids
Real-Life Practice: Sipping on Syrup
Part 2: Minding Your Meds: Administration and Calculation Methods
Chapter 5: The Prescription: Just What the Doctor Ordered
Comparing Written versus Electronic Medication Orders and Patient Charts
Identifying the Essential Ingredients of a Good Medication Order
Location, Location, Location: Knowing the Route of Administration
Timing Is Everything: Knowing When and How Often to Give a Med
Individualized Dosing Modifications
Verbal Orders: Make Like a Parrot and Repeat Them to the Provider
Real-Life Practice: Interpreting Orders
Real-Life Practice: Evaluating a Script
Chapter 6: Medication Labels and Patient Safety
Anatomy of a Medication Label
Highlighting the Four Big Patient Safety Concerns
Reviewing the Six “Rights” of Medication Administration
Chapter 7: Proper Medical Documentation and Dispensation
Reconciling Medications: Essential for Patient Care
The Medication Administration Record: Don’t Mar Your MAR!
Reviewing Medication Dispensation
Real-Life Practice: Administering a Narcotic
Real-Life Practice: Checking Vitals and Administering Fluids
Chapter 8: Mastering Calculation Methods for Dosing Meds
Taking a General Approach to Dosage Calculations
Focusing on the Formula Method
Relying on the Ratio-Proportion Method
Dosing with the Dimensional Analysis Method
Real-Life Practice: Using Various Methods for Common Dosage Calculations
Part 3: Calculations for Different Routes of Administration
Chapter 9: Oral Calculations: Tablets, Capsules, and Liquids
Checking Out the Label
Examining and Dosing Tablets
Considering the Colorful Capsule in Medical Dosing
Looking at Liquids and Knowing How to Dose Them
Converting from One Form of a Med to Another
Administering to the Patient with a Feeding Tube
Real-Life Practice: Doxycycline, the Infection Fighter
Chapter 10: Parenteral Injections and Calculations
Packing a Syringe: It’s Essential to be Equipped
Looking at the Label and Following Hospital Protocols
Practicing Parenteral Dosing Calculations
Real-Life Practice: Dosing an IM Med
Real-Life Practice: Dosing a Subcutaneous Med
Chapter 11: The IV League: Intravenous Dosing and Calculations
Infusion 101: Calculating Flow Rates, Infusion Times, and Drip Rates
Taking a Closer Look at IV Systems
Dosing Heparin, Insulin, and Other Infusions
Real-Life Practice: Finding the Drip Rate of a Dose of Albumin
Real-Life Practice: Calculating Infusion Time for D5W
Real-Life Practice: The Heparin Bolus and Maintenance Infusion
Chapter 12: Working with Reconstituted Solutions: It’s Like Magic
When Solute Met Diluent: A Love Story
Working through the Process of Reconstitution
Real-Life Practice: Reconstituting and Dosing Olanzapine
Real-Life Practice: Figuring the Dosage of Reconstituted Ampicillin
Real-Life Practice: Reconstituting and Dosing a Multiple-Strength Medication
Part 4: Dosing in Special Situations
Chapter 13: Insulin: Call It a Miracle Drug
Getting the Lowdown on Diabetes and Insulin
Measuring Insulin in Units
Getting the Most from the Dose with an Insulin Syringe
Combining Insulins
Using the Sliding Scale for Insulin Doses
Avoiding Confusion with the Continuous Infusion
Real-Life Practice: Administering an Insulin Infusion to Treat DKA
Real-Life Practice: Adjusting Insulin Levels Based on Glucose Levels
Chapter 14: Dosing for Two: The Pregnant Patient
Calculations for Pregnancy-Related Situations
Monitoring Mom and Junior When Administering Meds
Dealing with Medications That Aren’t Related to the Pregnancy
Real-Life Practice: Treating Hyperemesis Gravidarum
Real-Life Practice: Fighting Infection by Wiping Out the Germs
Real-Life Practice: Wiping Out Even More Germs
Chapter 15: Kid Stuff: Pediatric Calculations
Realizing the Dosing Differences from Child to Child and Adult to Child
Weighing and Going Metric: Dosing Meds for Kids
Trying Another Way: Calculating BSA
Considering Other Rules of Dosing
Looking at Special Considerations for Four Routes of Administration
Managing IV Fluids for Infants and Children
Being Extra Careful When Administering Meds or Fluids Intravenously
Real-Life Practice: Determining Whether an Ordered IV Dosage Is Safe
Real-Life Practice: Figuring a Ped Patient’s Fluid Needs
Real-Life Practice: Safely Administering an IV Infusion
Chapter 16: Adjusting Dosages for People in Special Situations
Keeping Up with the Kidneys
Dosing for Liver Disease
Leveling the Playing Field
Dosing for Patients Who Malabsorb Meds and Nutrients
Dosing for the Elderly
Real-Life Practice: Checking for Drug Interactions
Real-Life Practice: Dosing Meds to a Patient on HD
Chapter 17: Critical Care Dosing and Calculations
Being Prepared for Intensive Work in Intensive Care
Raising a Shockingly Low Blood Pressure
Lowering Skyrocketing High Blood Pressure
Dosing Meds That Fight Heart Failure
Treating a Dysrhythmia
Helping with Heparin
Real-Life Practice: Calculating Flow Rates of Nitroglycerin and Furosemide
Real-Life Practice: Finding the Initial Flow Rate for Nicardipine
Real-Life Practice: Determining the Flow Rate for Vasopressin
Chapter 18: Keeping a Patient Well-Nourished
Being Aware of a Patient’s Caloric Needs
Feeding through a Tube
Feeding through the Veins
Replacing Low Electrolytes
Real-Life Practice: Administering Furosemide and Replacing Lost Electrolytes
Real-Life Practice: Calculating a Patient’s Total Input
Part 5: The Part of Tens
Chapter 19: Ten Essential Dosing Calculations
Converting lb to kg and kg to lb
Converting mL to L and L to mL
Converting mg to g and g to mg
Calculating the mg Dose of Oral Meds
Calculating the mL Dose of Liquid Meds
Calculating Infusion Rates
Calculating Infusion Times
Calculating Infusion Volumes
Doing Parenteral Dosing Calculations
Doing Unit-Based Dosing Calculations
Chapter 20: Ten Ways to Avoid Common Dosing Mistakes
Watch Out for Meds That Sound Similar
Avoid Ambiguous Abbreviations
Assess a Med’s Applicability
Minimize Metric Mistakes
Check Infusion Rates
Avoid Measurement System Conversion Errors
Get the Timing Right When You Administer
Review the Allergies and ADRs
Don’t Forget the “Rights” of Medication Administration
Communicate!
Index
About the Authors
Connect with Dummies
End User License Agreement
List of Tables
Chapter 4
TABLE 4-1 Metric Prefixes and Abbreviations
TABLE 4-2 Apothecaries’ Unit Equivalents
TABLE 4-3 Metric-to-Metric Weight Conversion Factors
TABLE 4-4 Metric-to-Metric Liquid Volume Conversion Factors
TABLE 4-5 Metric-to-American Weight Conversion Factors
TABLE 4-6 Metric-to-American Liquid Volume Conversion Factors
TABLE 4-7 Metric-to-American Length Conversion Factors
TABLE 4-8 American-to-American Conversion Factors
TABLE 4-9 American-to-Metric Conversion Factors
TABLE 4-10 Apothecaries’ Conversion Factors
Chapter 5
TABLE 5-1 Meds with Confusing Similar Names
TABLE 5-2 Common and Accepted Dosage Abbreviations
TABLE 5-3 Unacceptable Abbreviations
TABLE 5-4 Interpreting Orders
List of Illustrations
Chapter 2
FIGURE 2-1: A number line.
FIGURE 2-2: A pill box.
Chapter 3
FIGURE 3-1: A pie with eight pieces.
Chapter 4
FIGURE 4-1: Metric units on a drug label.
FIGURE 4-2: A volumetric measuring glass with household and metric units.
FIGURE 4-3: Typical medicine dropper.
Chapter 5
FIGURE 5-1: Early ad for Bayer Aspirin.
FIGURE 5-2: Handwritten medication order for three meds.
Chapter 6
FIGURE 6-1: Label for donepezil HCI with brand name and generic name.
Chapter 9
FIGURE 9-1: Klonopin is the brand name for clonazepam in the United States.
FIGURE 9-2: A pill cutter.
Chapter 10
FIGURE 10-1: Syringes with different capacities.
FIGURE 10-2: Vials, ampules, and a Vacutainer.
Chapter 11
FIGURE 11-1: Schematic drawing of an IV setup.
FIGURE 11-2: An electronic infusion pump.
Chapter 12
FIGURE 12-1: Tobramycin label.
Chapter 13
FIGURE 13-1: An example of a blood glucose meter.
FIGURE 13-2: An example of an insulin product label.
FIGURE 13-3: A U-100 insulin syringe.
FIGURE 13-4: A prefilled insulin pen.
Chapter 15
FIGURE 15-1: A West nomogram.
FIGURE 15-2: A volume-control device.
Guide
Cover
Table of Contents
Title Page
Copyright
Begin Reading
Index
About the Authors
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Medical Dosage Calculations For Dummies®, 2nd Edition
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
Copyright © 2026 by John Wiley & Sons, Inc. All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies.
Media and software compilation copyright © 2026 by John Wiley & Sons, Inc. All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies.
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Introduction
Whether you’re currently working in a healthcare profession or studying in school, you’ve probably discovered that most healthcare jobs require some math — which is likely why you picked up this book.
Don’t panic if you’re intimidated by the mere mention of math. Most dosing math calculations are simple. At first glance, some dosing problems may seem pretty hard, but look closer. After you read them a few times, you’ll see that most seemingly complex calculations are really just a combination of simple calculations. After you read through the basics we cover in this book, you’ll hit your forehead with the heel of your palm whenever you come up against a challenging-on-the-surface problem and say, “Yes! Of course! I sorta knew that all along, but now I really get it!”
About This Book
This book puts a lot of medical dosing math into just a few chapters and in a very compact form. It’s different from other medical dosage math books in four main ways.
It’s all about dosing in the context of real medical conditions.
Our focus is on giving you the right math for real-life situations, not just presenting math problems. We bring up dosing scenarios you just might deal with every day in a medical-surgical unit or in a rehab or homecare setting.
It’s comprehensive.
It covers
all
the major areas in which you need to do dosing calculations. Other math books often don’t give you the broad coverage you need.
It offers a great review of math basics and then explains the three main dosing calculation methods.
We begin by looking briefly at numbers, arithmetic, fractions, units, and conversions, and then delve deeper into the more dosing-specific math you need to know to be a successful healthcare professional. We also offer many examples of solving dosing problems so you get plenty of practice.
It isn’t dull (we hope!), as other math books tend to be.
Because it’s a
For Dummies
book, you can be sure it’s easy to read and includes just enough humor to keep you entertained.
As you start reading, remember: This book is a reference. You can start anywhere you like and jump around as your interests and needs change. But it’s also a repair manual; it can help fill voids in your math background.
Some chapters are based on an aspect of medicine with particular dosing requirements (for example, pregnancy, insulin, and critical care), while others are based on particular methods of medication administration (for example, oral, injection, and intravenous). Some chapters also cover useful techniques, such as mixing insulin, splitting tablets, and managing an IV line. Regardless of the chapter’s particular focus, though, you get plenty of practical, real-life examples to help you hone your dosage calculation skills.
Note: Unlike many For Dummies books, this one doesn’t have a lot of light, humorous moments because so much in medical dosage calculations is critical. When patients’ lives are on the line, we’re certainly not going to make any jokes about the topics at hand.
Foolish Assumptions
As we wrote this book, we made the following assumptions about you:
We assume you’re in a two-year or four-year nursing program. But we also like the idea that you may be a working nurse, a concerned parent, or a caregiver.
We assume (or should we say, “hope”?) you learned some basic math in middle and/or high school.
But even if you missed some math concepts in school, you can find the ones you need for medical dosing in the review section of this book (Chapters 1 through 4). It’s amazing how little you need to review (for example, multiplying fractions and conversion math) to be caught up on the math you need to do dosing calculations.
We assume you’ll skip concepts you’re already comfortable with. That’s perfectly okay because this is a reference book, not a novel.
We assume you have access to a computer and the Internet. It’s not essential, but it’s very handy. Use a good search engine to find out more about any topic in this book — in the worlds of pharmacology, mathematics, and nursing practice.
Icons Used in This Book
We use several icons in this book to call out special kinds of information.
This icon represents information you definitely don’t want to skip over. It’ll come in handy as you do the medical dosage calculations throughout this book and in your career as a healthcare professional.
This icon highlights medical dosing problems that appear throughout each chapter. Each example describes a particular situation, asks one or two dosing questions, and then shows you the steps you need to take to get the answers.
This icon points out suggestions or recommendations. Don’t skip over the text marked with this icon if you want to know the quick and easy way to get things done.
The paragraphs next to this icon contain information that’s interesting and useful but not vital to your understanding of the topic at hand. This info may include a brief history of a principle, the earliest practitioners, or the origin of a word. This icon also showcases technical points. You can read the text marked with this icon or skip over it. Either is fine.
This is our “interesting trivia” icon. The text here usually contains odd facts, pieces of pop culture, bits of history, bizarre terms, or strange findings. You can read the info marked with this icon or skip over it.
Beyond the Book
In addition to the material in the print or ebook you’re reading right now, this book also comes with some access-anywhere goodies on the web. Check out the free Cheat Sheet for more on things like quick unit conversions and unacceptable medical abbreviations. To use the Cheat Sheet, simply go to www.dummies.com and search for “Medical Dosage Calculations For Dummies Cheat Sheet.”
Where to Go from Here
You can go to any chapter from here. The book isn’t linear, so you can start anywhere. First, check the table of contents, where you find the names of the parts and the chapters. Then pick any chapter you’re interested in.
If you can’t make a choice, begin with
Chapter 1
. It highlights the broad concepts covered in the book.
If you have a particular dosing problem you want to work on, find a chapter in the table of contents that deals with it, and go straight to it. You can always check out the index at the back of the book, too.
If, at any time, you get stuck on a concept, look for a cross-reference that tells you which chapter covers that particular topic. Then stop what you’re reading and go visit that chapter.
Part 1
Getting Up to Speed: Reviewing Math Basics
IN THIS PART …
Look at the importance of math in all healthcare fields.
Brush up on your basic math skills — including handling numbers and arithmetic.
Get familiar with fractions, percentages, and proportions.
Get the details about all the measurement systems and how to do conversions.
Chapter 2
Using Numbers and Arithmetic
IN THIS CHAPTER
Looking at the different numbers and numeral systems used in healthcare
Reviewing basic arithmetic — addition, subtraction, multiplication, and division
Working through some real-world dosing applications of basic math
In medicine, you use math daily. It doesn’t matter whether the initials after your name are DO, MD, RN, LVN/LPN, PA, or CNA (and that’s not the whole list by any means). Every professional in healthcare uses math. Your ability to do medical math well is essential in a hospital, but it also helps your patients and their caregivers when they’re discharged, and of course, the parents of your patients in pediatric cases. All these people rely on your medical dosing instructions.
So you’re not exactly great at math? Don’t worry! This chapter offers you a quick look at the different number systems you’ll see in healthcare and walks you through a quick review of arithmetic — that is, addition, subtraction, multiplication, and division. If you already have a firm grasp of the arithmetic we cover in this chapter, jump to Chapter 3 for more on fractions or Chapter 4 for more on systems of measurement and conversions. Then turn to Chapter 8 for specifics on the three methods of doing dosage calculations.
If you find that the math in this chapter is incomprehensible, consider getting a good, inexpensive math book, or just spend some time working on math on the Internet. Then come back to this chapter; the extra practice will help you get a better handle on the arithmetic basics that we cover here.
Healthy Numbers: Surveying the Numeral Systems Used in Healthcare
Healthcare professionals encounter two different numeral systems in their day-to-day lives: Arabic and Roman. Arabic numerals are the modern numbers (0–9) you’re likely familiar with. Roman numerals, which are more classical and more difficult to work with, make their way into medicine and real life, too. The following sections take a closer look at these two numeral systems and explain where they fit in healthcare.
What’s the difference between a number and a numeral? Well, at their simplest, numbers represent a basic quantity of something. Numerals, on the other hand, are the symbols or characters that represent the numbers.
Representing the classics: Roman numerals
Roman numerals are actually letters that represent numbers. The following list shows the common set of Roman numerals and the numbers they represent:
I
1
II
2
III
3
IV
4
V
5
VI
6
VII
7
VIII
8
IX
9
X
10
L
50
C
100
D
500
M
1,000
The Roman numeral system is decimal. It’s based on the concept of 10, 100, 1,000, and so on. But it’s not positional, meaning there’s no zero to serve as a placeholder. (See the section “Zeroing in on Zero: It’s really nothing” for details on zero’s place in math.)
Although Roman numerals are no fun for doing math, they still have a place in real life and medicine. For instance, you see them on the faces of older clocks, on the cornerstones of old buildings, in music chords, as suffixes to kings’ names (for example, Charles III), and to designate football games (for example, Super Bowl LIX). You also hear them in modern numbers and terms. For example, a $100 bill is often called a C note (which makes sense because the Roman numeral C stands for 100), and the U.S. mile gets its name from the Latin word mille, which means 1,000 (and the Roman numeral M stands for 1,000).
Modern medicine uses Roman numerals to describe dosages in grains, an older unit of measurement in the apothecaries’ system (see Chapter 4 for more details). Roman numerals also describe coagulation factors in the clotting system. For example, a Factor VIII (eight) deficiency is a primary cause of hemophilia. (In many cases, it’s a genetic disorder where the body doesn’t make clotting proteins like it’s supposed to.)
Making math a lot easier: Arabic numerals
Hindus likely invented Arabic numerals in about 500 CE. By 1000 CE, this new number system had made its way to Europe, and, by the 1200s, mathematicians like Leonardo Fibonacci of Pisa were big fans.
Arabic numerals have several advantages over Roman numerals. First, large numbers are much easier to write and calculate with. A single Arabic digit in the correct position can represent a very large number like 10,000,000, whereas you need 15 Roman numerals to represent a relatively small number like 3,888,000. Second, arithmetic is clumsy with Roman numerals. In fact, math lore is that if the ancient Greeks had used Arabic numerals, they would have invented calculus centuries before Sir Isaac Newton.
The Arabic numeral system has ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. Like Roman numerals, the Arabic numeral system is decimal, but as mentioned, it’s also positional. In a positional system, you have a ones column, a tens column, a hundreds column, and so on. Zero (0) is a placeholder when no value appears in a column.
TWO HIPPOCRATES FOR THE PRICE OF ONE
As you know, Hippocrates of Cos is considered to be the father of modern medicine. After all, he not only founded a medical school but is considered to be the author of the Hippocratic Oath that physicians today still swear to uphold. But he’s not the only famous Hippocrates to come out of Greece in the fifth century BCE. Hippocrates of Chios was a mathematician who was and still is famous for his theorems and work in early geometry.
You use Arabic numerals for the arithmetic calculations in this chapter and all the dosage calculations throughout the rest of the book. They work very nicely for all number types and all calculations (see the section “Ingesting a Dose of Numbers” for details on the main number types).
The metric system is a special set of Arabic numbers and is a heaven-sent gift to medical dosing calculations. In this system, each unit of weight or volume is a multiple of ten of another unit. Check out Chapter 4 for more on units of measurement and conversion.
Looking at where you see numbers in medicine
Numbers are everywhere in medicine, and, in general, they have the following three functions:
Reporting function:
Numbers describe patient basics — height, weight, pulse, and blood pressure. These measurements tell you a lot about the patient’s condition, and you make clinical decisions based on them. Numbers also indicate vital signs on a patient’s monitor. Knowing the significance of these different reporting numbers is essential in your work.
Identification function:
Patient numbers identify patients, and medication numbers identify medications. Identification numbers are vital in dosing meds because you must always give the right medication to the right patient.
Calculation function:
Numbers (and this is quite important) explicitly describe the amounts of medications that you administer to patients. Dosing calculations use relatively simple math, while the calculations used in disease research and the development of pharmaceuticals are considerably more complex.
Ingesting a Dose of Numbers
For a system with only ten digits, Arabic numbers sure have a lot of names. In case you don’t remember everything you learned during your middle school days, here’s a quick look at the main types of numbers you need to know:
Natural numbers:
All the positive whole numbers (also called
counting numbers
), beginning at 1 and going on forever
Integers:
All the natural numbers, as well as zero and negative numbers
Rational numbers:
All the integers, as well as all numbers that can be expressed as a ratio of two numbers, including all common and decimal fractions (see
Chapter 3
)
Irrational numbers:
All the numbers that can’t be expressed as ratios, including the square root of ( and pi (π)
Real numbers:
All rational and irrational numbers
Imaginary numbers:
A special number type, dealing with the square root of , developed by Gerolamo Cardano and other Italian mathematicians in the 16th century to determine the roots of cubic and quartic polynomials; currently useful in fluid dynamics, quantum mechanics, and relativity
The following sections describe a number line (a way of visualizing numbers) and zero (a fundamental concept in mathematics).
Visualizing numbers on the number line
A number line is a graphic representation of the array of real numbers. A number line has 0 in the center, positive numbers to the right of 0, and negative numbers to the left of 0.
The number line in Figure 2-1 shows the full set of integers. (Fractions and irrational numbers fall between the integers on the number line.) It stretches to infinity at both the left and the right. The farther to the right of 0 on the number line you go, the larger the numbers get in value. The farther to the left of 0 you go, the more the numbers decrease in value.
FIGURE 2-1: A number line.
When it comes to numbers, looks can be deceiving. For example, the 9 in –9 has a larger magnitude (the value without the sign, also called absolute value) than the 8 in –8, but the minus sign (–) tells you that –8 is actually larger than –9. A “larger” negative number has less value than a “smaller” negative number. Confusing? The number line can help you visualize it.
Zeroing in on zero: It’s really nothing
Zero is an abstract concept. For example, you can’t have zero bananas (or any other object). Well, if you have one banana and somebody takes it, you have the concept of zero — even though you no longer have the banana. As the old song goes, “Yes, we have no bananas.”
Zero is also a placeholder in positional numeral systems, like the Arabic numeral system (see the earlier section “Making math a lot easier: Arabic numerals” for details). When you see a number with 0 (for example, 103), the 0 represents a column with no number in it. The number 103 has 1 in the hundreds column, 0 in the tens column, and 3 in the ones column.
When you write fractional decimals, be sure to write a zero before the decimal point. It’s better notation in medical dosing to describe half a mL as 0.5 mL rather than .5 mL. As you can see, the notation .5 mL could easily be misread as 5 mL. Adding the zero makes the notation clearer.
Using Addition to Make Everything Add Up
Addition is the process of adding one or more quantities to another quantity. (The result of a problem is called the sum.) Also, you can add the terms in any order, thanks to the mathematical property called commutativity, which means that changing the order of something does not change the end result. For example:
To do simple addition, first put the numbers in a column. Start by adding the numbers in the ones column (the one on the far right). You can add a column of numbers from the top to the bottom or from the bottom to the top. The result is the same.
If the sum of the numbers in a column exceeds ten, you must carry the left digit of the two-digit answer to the next column. In other words, write the right digit of the two-digit answer beneath the column you’re adding, and write the left digit above the next column to the left, like so:
