### Lesson plan

# Subtraction with Regrouping

#### Learning Objectives

Students will be able to use two different strategies to subtract three-digit numbers.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.

#### Introduction

*(5 minutes)*

- Write the following problem on the board:
**365 – 174**. - Distribute the whiteboards and ask students to solve the problem using a strategy of their choice. Then, ask students to turn to their elbow partner to compare strategies and answers.
- Choose students who used different strategies to share their steps to solve the problem.
- Solve the problem on the board using
**expanded form subtraction**and highlight that you have to regroup. Define**regrouping**as changing groups of ones, tens, or hundreds into another value (e.g., changing 1 ten to 10 ones). - Explain that they'll learn two strategies for solving subtraction problems to help them check their answers and better understand subtraction processes.

#### Explicit Instruction/Teacher modeling

*(8 minutes)*

- Model completing the first problem using expanded form subtraction from the Three-Digit Subtraction, Part 1 worksheet. Explain that expanded notation subtraction is a strategy to subtract larger numbers by decomposing the numbers into their values (e.g.,
**156 = 100 + 50 + 6**), stacking them on top of one another, subtracting them one column at a time from right to left, and finally adding the differences to get the total remaining. - Ask partners to look at the problem you solved and explain to each other the steps you used to solve the problem.
- Model completing the first problem using standard algorithm subtraction. Explain that
**standard algorithm subtraction**is subtraction where digits in each number are lined up based on their place value and subtracted one place value at a time, starting from the right to the left.

#### Guided Practice

*(15 minutes)*

- Choose a student to model the next problem for the class. Correct and offer suggestions throughout the whole process. Allow other students to share ideas as well.
- Distribute the Three-Digit Subtraction, Part 1 worksheet and ask students to solve the rest of the problems in partners. Remind them they'll have to regroup (i.e., borrow from a higher place value to add to a lesser place value) to complete the subtraction problem.
- Have two pairs compare their answers, and allow them to adjust them as necessary.
- Choose students to share the difference between the two strategies, and to decide which they prefer to use when subtracting three-digit numbers.

#### Independent working time

*(12 minutes)*

- Distribute the Three-Digit Subtraction, Part 2 worksheet and review the instructions.
- Have students complete the whole worksheet, and then compare their answers with their partners. If they have varying answers, ask them to change the answer and write a sentence about what they had to adjust.

#### Differentiation

**Support:**

- Allow students to use place value charts and base ten blocks as they complete the two subtraction strategies.
- Have them practice regrouping with two-digit numbers using the exercise Two-Digit Subtraction and Regrouping. Hand out paper for their work on both of the subtraction strategies.

**Enrichment:**

- Challenge students with word problems in the exercise Three-Digit Subtraction Word Problems. Ask them to show their strategies on a sheet of paper.
- Pair advanced students with those who need additional support. Ask advanced students to explain their processes during the group work and to check their partner's answers for accuracy.

#### Assessment

*(5 minutes)*

- Write the following problem on the board:
**809 – 312**. Distribute the index cards and ask students to solve the problem using the standard algorithm and expanded notation subtraction strategies. - Use the index card as a formative assessment of their ability to regroup to solve subtraction problems.

#### Review and closing

*(5 minutes)*

- Provide an incorrect subtraction example. Have students decide if it's incorrect and why. Allow them to use their whiteboards to solve the problem and then explain the error.
- Ask this question: "What are the benefits of knowing more than one way to subtract three-digit numbers?"
- Have students share and discuss in partners. Then, summarize for the class some of the responses you heard during their discussions.