Math Mammoth Add & Subtract 2-C

Math Mammoth Add and Subtract 2-C focuses on regrouping in addition (a.k.a. carrying) and in subtraction (a.k.a. borrowing), on a second-grade level. The book assumes the student has already learned to add two-digit numbers with regrouping. In this book, students will learn 3-digit addition with regrouping, and both 2- and 3-digit subtraction with regrouping, with these exceptions: this book does not cover regrouping over zero tens in subtraction, nor regrouping twice in subtraction. Those topics are found in the book Add & Subtract 3.In the first lesson, the student adds three-digit numbers with a regrouping in tens, but there is no regrouping in hundreds. Students already know how to regroup two-digit numbers, so this lesson simply extends that knowledge to numbers with three digits.In the next lesson, students regroup 10 tens as a hundred (or carry to the hundreds). This is first illustrated with a visual model. You can adapt the exercises in the lesson to be done with manipulatives instead, if desired.Then we study regrouping twice in addition: 10 ones form a new ten, and then 10 tens form a new hundred. Again, students first work with visual models, with the aim of helping them to understand the concept itself. Then, they learn the abstract process, adding the numbers in columns.Next, we study regrouping in subtraction, starting with two-digit numbers. First, students are taught to break one ten into 10 ones. For example, 5 tens 4 ones is written as 4 tens 14 ones; one of the tens is “broken down” into 10 ones. This is the process of regrouping: one of the tens “changes groups” from being with the tens to being with the ones.After mastering that process, it is time to use regrouping in subtraction problems and learn the traditional paper-and-pencil method of subtracting (where one number is written under the other).Next, there is a lesson on word problems that include the thought of “more” or “fewer”, and also several techniques or “tricks” for mental subtraction. The word problem sets in the book typically include both addition and subtraction problems. The reason for this is that students need to learn to recognize whether a problem requires addition or subtraction, and not blindly apply the operation mentioned in the title of the lesson.After this, it is time to study regrouping in subtraction with three-digit numbers. There are four cases:Regrouping one ten as 10 ones, such as is necessary in 546 − 229.Regrouping one hundred as 10 tens, such as is necessary in 728 − 441.Regrouping two times (one ten as 10 ones, and one hundred as 10 tens), such as in 725 − 448.Regrouping with zero tens, such as is necessary in 405 − 278.Since this book is geared towards second grade, we only study cases (1) and (2) from the list above. The other two cases are left for third grade; you can find lessons for those in our Blue Series book Add & Subtract 3).Lastly, students work with bar graphs and play Euclid’s game, which is meant as a fun, supplemental lesson.The answer key is appended.There are free videos that match the book at https://www.mathmammoth.com/videos/. Choose 2nd grade, chapter 8. Read more