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Math Mammoth Decimals 1

Math Mammoth Decimals 1 math book cover
69 pages
(answers included)

Sample pages (PDF)
Contents and Introduction
Adding and Subtracting
with Tenths

Comparing
Rounding to the Nearest
Whole Number


Prices & ordering

PDF download $3.50

Buy at Kagi
(credit cards, Paypal, check, cash, PO, wire transfer, money order; Kagi shopper help)

Buy at Currclick
(credit cards, Paypal)


Printed copy $11.20, b&w

Buy at Lulu
(credit cards, Paypal, PO)

Buy at Currclick
(credit cards, Paypal)

small flag of SpainEste libro en español

Math Mammoth Decimals 1 is an introduction to decimal numbers, and is best suited for 4th to 5th grade math.

The PDF version of this book is enabled for annotation. This means that if you prefer, your student can fill it in on the computer, using the typewriter and drawing tools in Adobe Reader version 9 or greater.

This book deals with decimal numbers that have tenths and hundredths - numbers with a maximum of two decimal digits. We only deal with some of the basic operations: addition, subtraction, and multiplication by a whole number, with a strong emphasis on mental calculations. The idea is to lay a solid conceptual foundation so that the student does not succumb to rote memorization of rules and procedures without understanding.

The two operations not studied in this book are multiplying a decimal by a decimal and decimal division. Those can be found in Math Mammoth Decimals 2.

We use number lines, fraction models, and place value charts to teach the concepts of tenths and hundredths. In studying addition and subtraction, we compare decimal operations with corresponding fraction operations in order to show why they work.

A common student error is to add 0.4 + 0.8 = 0.12. Here, the student may be considering the decimal part of a number as a 'separate whole number', and try to apply whole number arithmetic within the decimal part. To help such a student, read the decimals as fractions and emphasize how fractions are added. Think: four tenths plus eight tenths equals twelve tenths, which is 1.2.

When we add decimals of different "length" (numbers with different amounts of decimal digits), such as 0.4 + 0.08, you can "tag" a zero to the end of 0.4 to make adding easier. The problem becomes 0.40 + 0.08. Now, both addends have hundredths, so the answer is simply 48 hundredths or 0.48. This is the same thing as converting the corresponding fractions (four tenths and eight hundredths) to have the same denominator (forty hundredths and eight hundredths).

Other topics covered are comparing decimals, multiplying a decimal by a whole number, rounding, estimating, and money problems.

Several videos from my Decimal arithmetic playlist can be used in conjunction with this book.


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From a homeschooling parent who has used Decimals 1 with a 5th grader:

My 5th grader and I worked through the decimals book. It actually helped me to understand decimals a lot better also. We were both amazed at how easy they are to work with once you understand the concepts behind them.

I love the books. They include a lot of thinking and reasoning skills that our other math program did not include. They also present things in a simple clear manner. No more tears when it comes to decimals!!!

Michele Cutlip

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You can buy Math Mammoth books at:

  • Kagi store - all of the downloads and CDs. I maintain several order pages at Kagi:

    Kagi accepts all major credit cards, Paypal (USD), checks, cash, money orders, purchase orders, wire transfers, TrialPay, and even cash. Read more about the payment methods here. Please see Kagi Shopper Help for any other questions about the ordering process.

    After completing the order at Kagi, you will see the download links on the receipt page. You will also receive an email with download links for each book you bought, or for a zip file for the packages. You click on the links and download the books to your computer's hard drive.

    In case of any problems with the download, you can always email me, and I can email the books to you directly. My contact info will be in the email you receive.


  • CurrClick.com carries all Blue, Golden, and Light Blue series books as downloads. They accept credit cards and Paypal. You will be able to download the products immediately upon the purchase, and also return to your account at CurrClick to redownload.

  • Lulu offers printed copies for the Blue, Golden, and Light Blue series books.

  • Rainbow Resource carries printed copies for the Light Blue series books, plus Light Blue CDs. You can also find links to Rainbow Resource on the individual product pages on this site.

By purchasing any of the books, permission IS granted for the teacher (or parent) to reproduce this material to be used with his/her students in a teaching situation; not for commercial resale. However, you are not permitted to share the material with another teacher.

In other words, you are permitted to make copies for the students/children you are teaching, but not for other teachers' usage.


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