Today we look at Math in Focus 3A Lesson 4.3 Subtraction with Regrouping. I was planning for a lesson I will be teaching to third graders at The Blake School in Hopkins, MN.
The main method (which is in the textbook) is to develop an understanding of the standard algorithm, which is essentially about regrouping / renaming a numbers to facilitate subtraction.
The alternate method (which is not in the book) is to get students to see 2,598 as 2,500 + 98 ... which make subtraction from 5,000 + 100 + (46) fairly straight forward. 46 can be put aside.
The choice of numbers in this anchor task allows for the alternate method (which teachers may get advanced students to think about) while letting the other students have ample time to master the main method.
The choice of numbers allows emphasis on doubles facts (4,000 - 2,000, 1,000 - 500 and 16 - 8).
It is important for teachers, in the lesson planning process to think about the choice of examples selected.
Grade 4 Lesson