# Lesson 1

### Lesson Purpose

The purpose of this lesson is for students to add and subtract within 100 without composing or decomposing a ten. Students find sums and differences in a way that makes sense to them and compare methods based on place value and the relationship between addition and subtraction.

### Lesson Narrative

Up to this point, students have only subtracted multiples of ten from other two-digit numbers within 100. In this lesson, students build on their work with interpreting bar graphs and solving Compare story problems to add and subtract within 100 with larger numbers. The representations presented in both activities (bar graphs and connecting cubes) invite students to use and connect a variety of different methods and prepare them for subtraction methods based on place value.
• Engagement

### Learning Goals

Teacher Facing

• Add and subtract within 100 in a way that makes sense to them without composing or decomposing a ten.
• Solve problems within 100.

### Student Facing

• Let’s solve Compare problems with larger numbers.

### Required Preparation

Activity 1:

• Create towers of 10 with the connecting cubes.
• Have single connecting cubes available.

Activity 2:

• Create towers of 10 with the connecting cubes.
• Have single connecting cubes available.

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

In grade 1, students used connecting cubes to understand a ten as a group of 10 ones. How did using the connecting cubes in today's lesson help students consider strategies based on place value when adding or subtracting?

### Suggested Centers

• Capture Squares (1–3), Stage 1: Add within 10 (Supporting)
• Five in a Row: Addition and Subtraction (1–2), Stage 5: Add within 100 without Composing (Supporting)