# Lesson 8

Subtraction Algorithms (Part 1)

### Lesson Purpose

The purpose of this lesson is for students to use their knowledge of base-ten diagrams to make sense of a written subtraction algorithm.

### Lesson Narrative

In previous lessons, students revisited subtraction within 1,000 using strategies based on place value, properties of operations, and the relationship between addition and subtraction. In this lesson, students are introduced to a subtraction algorithm that clearly shows the subtraction of ones from ones, tens from tens, and hundreds from hundreds, and is similar to one of the initial addition algorithms in a prior lesson. Students should have access to base-ten blocks as needed.

• Engagement
• MLR8

### Learning Goals

Teacher Facing

• Relate base-ten diagrams to written algorithms for subtraction.

### Student Facing

• Let’s learn a new way to subtract.

### Required Materials

Materials to Copy

• Diagrams and Algorithms

### Required Preparation

Activity 2:

• Create a set of cards from the blackline master for each group of 2.

### Lesson Timeline

 Warm-up 10 min Activity 1 15 min Activity 2 20 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

Reflect on how comfortable your students are asking questions of you and of each other. What can you do to encourage students to ask questions?