Math Mammoth Add & Subtract 2-B

77 pages
(includes answers)

Sample pages (PDF)
Contents & Introduction
Adding with Whole Tens
Going Over Ten
Two-Digit Numbers Ending in 9

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Este libro en español

Math Mammoth Add & Subtract 2-B is a continuation to the book Math Mammoth Add & Subtract 2-A. The lessons in this book focus, first of all, on mental addition and subtraction of two-digit numbers, and secondarily on regrouping in addition (two-digit numbers). The sequel to this book, Math Mammoth Add & Subtract 2-C, teaches regrouping in subtraction with two-digit numbers and regrouping in both addition and subtraction with three-digit numbers, with some exceptions.

This book includes many lessons that practice mental math, which is important because it builds number sense. Number sense is the ability to work with numbers flexibly, breaking them apart and combining them, for the purpose of calculating with them. Number sense has been shown to be a predictor of future success in algebra, showing its importance.

Some examples of the types of mental math taught in the book are:

• Solving 23 + 6 or 45 + 2 by comparing them to the corresponding sums without the tens: 3 + 6 and 5 + 2.
• Similarly, solving 47 − 5 and 69 − 8 by solving 7 − 5 and 9 − 8 first.
• Subtracting a single-digit number from a multiple of ten: 60 − 5 or 40 − 9.
• Adding and subtracting two-digit numbers when one of them is a multiple of ten (such as 30 + 14 or 66 − 20).
• Adding a two-digit and a single-digit number mentally when the sum crosses to the next ten: 25 + 6 or 47 + 8.

After the lessons that focus on mental math, students learn how to add two-digit numbers with regrouping. This is explained in detail with the help of visual models (base-ten blocks). You are welcome to use actual physical base-ten blocks, if you prefer. The main concept is that 10 ones are regrouped to form a new ten, and this new ten is written using a little “1” in the tens column.

The book concludes with the topics of adding three or four numbers, both mentally and in columns.

You can find videos to match with the topics of this book at our 2nd grade math videos page, in the sections for Chapter 1 and Chapter 4

The PDF version of this book can be filled in on a computer, phone, or tablet, using the annotation tools found in many PDF apps. See more.

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