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Copyright 2005 LearningExpress, LLC. All rights reserved under International and Pan-American Copyright Conventions. Published in the United States by LearningExpress, LLC, New York. Library of Congress Cataloging-in-Publication Data: Practical math success in 20 minutes a day.3rd ed. p. cm. Rev. ed. of: Practical math success in 20 minutes a day / Judith Robinovitz. 2nd ed. 1998. ISBN 1-57685-485-X 1. Mathematics. I. Robinovitz, Judith. Practical math success in 20 minutes a day. II. Title: Practical math success in twenty minutes a day. QA39.3.P7 2005 510'.7dc22 2005040830 Printed in the United States of America 9 8 7 6 5 4 3 2 1 Third Edition ISBN 1-57685-485-X For information on LearningExpress, other LearningExpress products, or bulk sales, please write to us at: LearningExpress 55 Broadway 8th Floor New York, NY 10006 Or visit us at:


INTRODUCTION How to Use This Book PRETEST LESSON 1 Working with Fractions Introduces the three kinds of fractionsproper fractions, improper fractions, and mixed numbersand teaches you how to change from one kind of fraction to another Converting Fractions How to reduce fractions, how to raise them to higher terms, and shortcuts for comparing fractions Adding and Subtracting Fractions Adding and subtracting fractions and mixed numbers and nding the least common denominator Multiplying and Dividing Fractions Focuses on multiplication and division with fractions and mixed numbers Fraction Shortcuts and Word Problems Arithmetic shortcuts with fractions and word problems Introduction to Decimals Explains the relationship between decimals and fractions Adding and Subtracting Decimals Deals with addition and subtraction of decimals, and how to add or subtract decimals and fractions together

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Multiplying and Dividing Decimals Focuses on multiplication and division of decimals Working with Percents Introduces the concept of percents and explains the relationship between percents and decimals and fractions Percent Word Problems The three main kinds of percent word problems and real-life applications Another Approach to Percents Offers a shortcut for nding certain kinds of percents and explains percent of change Ratios and Proportions What ratios and proportions are and how to work with them Averages: Mean, Median, and Mode The differences among the three measures of central tendency and how to solve problems involving them Probability How to tell when an event is more or less likely; problems with dice and cards Dealing with Word Problems Straightforward approaches to solving word problems Backdoor Approaches to Word Problems Other techniques for working with word problems Introducing Geometry Basic geometric concepts, such as points, planes, area, and perimeter Polygons and Triangles Denitions of polygons and triangles; nding areas and perimeters

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Quadrilaterals and Circles 181 Finding areas and perimeters of rectangles, squares, parallelograms, and circles Miscellaneous Math Working with positive and negative numbers, length units, squares and square roots, and algebraic equations 191

POSTTEST GLOSSARY APPENDIX A APPENDIX B Dealing with a Math Test Additional Resources

203 213 215 221


How to Use This Book

his is a book for the mathematically challengedfor those who are challenged by the very thought of mathematics and may have developed calculitis, too much reliance on a calculator. As an educational consultant who has guided thousands of students through the transitions between high school, college, and graduate school, I am dismayed by the alarming number of bright young adults who cannot perform simple, everyday mathematical tasks, like calculating a tip in a restaurant. Some time ago, I was helping a student prepare for the National Teachers Examination. As we were working through a sample mathematics section, we encountered a question that went something like this: Karen is following a recipe for carrot cake that serves 8. If the recipe calls for 3 of a cup of our, how much our does she 4 need for a cake that will serve 12? After several minutes of confusion and what appeared to be thoughtful consideration, my student, whose name also happened to be Karen, proudly announced, Id make two carrot cakes, each with 3 of a cup of our. After dinner, Id throw away the leftovers! 4 If youre like Karen, panicked by taking a math test or having to deal with fractions, decimals, and percentages, this book is for you! Practical Math Success in 20 Minutes a Day goes straight back to the basics, reteaching you the skills youve forgottenbut in a way that will stick with you this time! This book takes a fresh approach to mathematical operations and presents the material in a unique, user-friendly way so youll be sure to grasp the material.


Overcoming Math AnxietyDo you love math? Do you hate math? Why? Stop right here, get out a piece of paper, and write the answers to these questions. Try to come up with specic reasons that you either like or dont like math. For instance, you may like math because you can check your answers and be sure they are correct. Or you may dislike math because it seems boring or complicated. Maybe youre one of those people who dont like math in a fuzzy sort of way but



cant say exactly why. Now is the time to try to pinpoint your reasons. Figure out why you feel the way you do about math. If there are things you like about math and things you dont, write them both down in two separate columns. Once you get the reasons out in the open, you can address each oneespecially the reasons you dont like math. You can nd ways to turn those reasons into reasons you could like math. For instance, lets take a common complaint: Math problems are too complicated. If you think about this reason, youll decide to break every math problem down into small parts, or steps, and focus on one small step at a time. That way, the problem wont seem complicated. And, fortunately, all but the simplest math problems can be broken down into smaller steps. If youre going to succeed on standardized tests, at work, or just in your daily life, youre going to have to be able to deal with math. You need some basic math literacy to do well in lots of different kinds of careers. So if you have math anxiety or if you are mathematically challenged, the rst step is to try to overcome your mental block about math. Start by remembering your past successes. (Yes, everyone has them!) Then remember some of the nice things about math, things even a writer or artist can appreciate. Then youll be ready to tackle this book, which will make math as painless as possible.Build on Past Success

Think back on the math youve already mastered. Whether or not you realize it, you already know a lot of math. For instance, if you give a cashier $20.00 for a book that costs $9.95, you know theres a problem if she only gives you $5.00 back. Thats subtractiona mathematical operation in action! Try to think of several more examples of how you unconsciously or automatically use your math knowledge. Whatever youve succeeded at in math, focus on it. Perhaps you memorized most of the multiplication table and can spout off the answer to What is 3 times 3? in a second. Build on your successes with math, no matter how small they may seem to you now. If you can master simple math, then its just a matter of time, practice, and study until you master more complicated math. Even if you have to redo some lessons in this book to get the mathematical operations correct, its worth it!Great Things about Math

Math has many positive aspects that you may not have thought about before. Here are just a few: 1. Math is steady and reliable. You can count on mathematical operations to be constant every time you perform them: 2 plus 2 always equals 4. Math doesnt change from day to day depending on its mood. You can rely on each math fact you learn and feel condent that it will always be true. 2. Mastering basic math skills will not only help you do well on your school exams, it will also aid you in other areas. If you work in elds such as the sciences, economics, nutrition, or business, you need math. Learning the basics now will enable you to focus on more advanced mathematical problems and practical applications of math in these types of jobs. 3. Math is a helpful, practical tool that you can use in many different ways throughout your daily life, not just at work. For example, mastering the basic math skills in this book will help you to complete practical tasks, such as balancing your checkbook, dividing your long-distance phone bill properly with your roommates, planning your retirement funding, or knowing the sale price of that sweater thats marked down 25%. 4. Mathematics is its own clear language. It doesnt have the confusing connotations or shades of meaning that sometimes occur in the English language. Math is a common language that is straightforward and understood by people all over the world.



5. Spending time learning new mathematical operations and concepts is good for your brain! Youve probably heard this one before, but its true. Working out math problems is good mental exercise that builds your problem-solving and reasoning skills. And that kind of increased brain power can help y