Laura Laing - Math for Grownups: Relearn the Arithmetic You Forgot from School

Relearn the Arithmetic You
Forgot from School So You Can:

Calculate how much that raise will
really amount to (after taxes)

Figure out if that new fridge will actually fit

Help a third grader with his fraction homework

Convert calories into cardio time

LAURA LAING
BS, Math Educator

Copyright 2011 by F+W Media, Inc.
All rights reserved.

This book, or parts thereof, may not be reproduced in any
form without permission from the publisher; exceptions are
made for brief excerpts used in published reviews.

Published by
Adams Media, a division of F+W Media, Inc.
57 Littlefield Street, Avon, MA 02322. U.S.A.
www.adamsmedia.com

ISBN 10: 1-4405-1263-9
ISBN 13: 978-1-4405-1263-6
eISBN 10: 1-4405-2689-3
eISBN 13: 978-1-4405-2689-3

Printed in the United States of America.

10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data
Laing, Laura.
Math for grownups / Laura Laing.
p. cm.
Includes index.
ISBN 978-1-4405-1263-6
1. Mathematics-Popular works. I. Title.
QA93.L27 2011
510-dc22
2011010369

This publication is designed to provide accurate and authoritative information with regard to the subject matter covered. It is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional advice. If legal advice or other expert assistance is required, the services of a competent professional person should be sought.

From a Declaration of Principles jointly adopted by a Committee of the
American Bar Association and a Committee of Publishers and Associations

Many of the designations used by manufacturers and sellers to distinguish their product are claimed as trademarks. Where those designations appear in this book and Adams Media was aware of a trademark claim, the designations have been printed with initial capital letters.

This book is available at quantity discounts for bulk purchases.
For information, please call 1-800-289-0963.

For my three favorite mathematicians:
Dad, Gina, and Zoe.

INTRODUCTION :
Everyday Math: Easier Than Running Out of Paint

1 AT THE STORE:
Deal or No Deal?

2 AT THE DEALERSHIP:
Leasing vs. Buying, New vs. UsedYou Do the Math

3 ON THE MARKET:
Buying a House by the Numbers

4 AT HOME:
Will Your New Fridge Fit?

5 IN THE KITCHEN:
Making More, Making LessRecipe
Math to the Rescue!

6 IN THE YARD:
If a Train Leaves Omaha at 8 A.M. ,
How Much Lawn Edging Do You Need?

7 IN THE CRAFT ROOM:
Measure Twice, Cut Once

8 AT THE BANK:
Income Minus Expenses Equals Happiness (or Misery)

9 IN THE GYM:
How Many Miles on the Treadmill to
Burn Off One Doughnut?

10 ON THE ROAD:
When Will You Get There and
How Much Will You Spend?

The numbers game plays a starring role in almost every part of daily life, from making dinner to planning a weekend getaway. Heck, you need math to order a pizza.

Even people who dont sweat math problemsnamely, mathematicians!sometimes have trouble with the calculations we face in everyday life. So its no wonder that those of us who have already forgotten what we learned in high school (or, worse, never liked math and didnt do well in it) can sometimes stare at a math problem and not have the faintest idea what to do about it.

But luckily you dont have to be Stephen Hawking (or even be proficient with a scientific calculator) to use math in ordinary situations. Remember, its only a tool. (And its not even one that requires safety glasses or special training so you wont cut off the tip of your left index finger.) Its a language that describes how our world fits together. Math enables us to make predictions and quick decisions. Math helps us feel powerful and confident.

Heres the honest truth: Adding fractions is no harder than signing up for the office football pool or buying airline tickets online or remembering how to create a folder on your computer desktop. It may just seem more challenging.

The truth is that very few people in the world cant do math. You are not one of them. Heres the thingmost math doesnt require you to remember how to find the slope of a line (or even to remember what slope is). The everyday stuff is a combination of basic arithmetic and your innate understanding of how to speak the language of numbers, shapes, and measurements.

Yep, innate. You were born with curiosity about the world around you. Math is just one way to describe that world. And, like it or not, its a pretty important way.

So unless you dont care whats in your bank account or whether your new elliptical machine will fit through the door of your exercise room, youre going to have to do some math.

And you might as well think youre good at it, right? (Because, guess what? You are.)

You dont have to know calculus to figure out how to lower your monthly mortgage payments. You dont have to remember the Pythagorean Theorem to lose a few extra pounds. And you dont have to do long division in your head to buy paint for your new house.

You do need to have an open mind and a sense of humor. After all, its only math.

Unless you just hit the Lotto jackpot, youre probably looking for ways to save a little cash at the register. Whether youre buying groceries or the perfect knickknack for your newly decorated living room, keeping more money in your wallet can be a real challenge. The key is to plan ahead and stay sharp.

Whats more important: finding your servers tip to the penny or getting out of the restaurant with your sanity intact? We all know some of those folks who obsessively use a calculator to find the tip on their morning bagel and coffee, but how much fun are they? (And how much fun are they having?)

Estimation is your best friend. Need to split the lunch bill with your best friends? Estimate. Need to know how far apart to plant your begonias? Estimate. Want to know how long it will take you to get to Grandmas house for Thanksgiving dinner? Estimate.

When you estimate, you create math problems that are simple to solve in your head. You round numbers so that theyre easy to add, subtract, multiply, or divide. You evaluate what you can do well and apply those strategies to the problem at hand. In short, you look for ways to do mental math.

But you are not guessing. In some instances, youre finding a range of possible solutions that make sense. (Whats my ETA?) In other situations, youre merely figuring out the answer to a yes-or-no question. (Can I afford to buy those designer shoes?) And sometimes you just dont need to have the answer down to the penny. (How much can I expect to pay each month for my mortgage?)

Mathematicians and scientists estimate all the timeeven when theyre looking for an exact answer. Estimating helps you judge your solution, and this in turn can keep you out of embarrassing situations (like arriving at the party way too late) and hot water (like paying more than you can afford for your not-so-smart phone).

Estimating can really pay off when youre in a hurry. And lets face it, who doesnt want to get out of the grocery store as quickly as possible? The carts squeaky wheel would drive Buddha to distraction.