# 10. Three-digit subtraction with regrouping (A)

## About this lesson

Lesson objective: Add and subtract two three-digit numbers involving regrouping using place value strategies and the relationship between addition and subtraction.

This lesson provides an opportunity for students to apply their knowledge and understanding of three-digit addition and subtraction to a real-life situation. Students are asked to find out how many pieces of candy are in each colored jar, and how close Kate's estimate was to the total amount of candy.

Key Concepts students will use:

- Subtraction strategies used with two-digit numbers can be used with three-digit numbers (regrouping).
- Subtraction problems can be thought of as missing addend problems.

Skills students will use:

- Add and subtract numbers within 1,000 using knowledge of place value and properties of operations
- Add and subtract numbers within 100 using knowledge of place value (Grade 2, Unit 1)
- Represent three-digit numbers in different but equivalent ways (Grade 2, Unit 6)

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they apply regrouping strategies used to solve two-digit subtraction with three-digit subtraction equations, using base ten blocks and number lines as tools to demonstrate their thinking.

**Key vocabulary: **

- base ten blocks
- decompose
- digit
- equivalent
- hundreds
- number line
- ones
- place value
- regroup
- tens