# Lesson 7

Subtract Two Digits

### Lesson Purpose

The purpose of this lesson is for students to subtract a two-digit number from a two-digit number when a ten is decomposed when subtracting by place.

### Lesson Narrative

In previous lessons, students learned that decomposing a ten is sometimes necessary when subtracting two numbers. Students used connecting cubes and base-ten blocks to represent their methods when subtracting a one-digit number from a two-digit number.

In the fist activity, students use methods that make sense to them to subtract and compare their methods with a partner. In the activity synthesis, students make connections across different methods and representations and consider which tools and representations work best for them. In the second activity, students use base-ten blocks to represent expressions and decompose a ten when subtracting by place.

Students should have access to connecting cubes and base-ten blocks throughout the lesson and the cool-down.

• Representation

### Learning Goals

Teacher Facing

• Subtract a two-digit number from a two-digit number in a way that makes sense to them.

### Student Facing

• Let’s subtract with two-digit numbers.

### Required Materials

Materials to Gather

Materials to Copy

• Using Blocks to Take Away

### Required Preparation

Activity 2:

• Create a set of cards from the blackline master for each group of 4.

Building Towards

### 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

How are base-ten blocks and diagrams supporting students in showing what they understand about decomposing a ten when subtracting by place?