# Lesson 15

Decompose a Ten and a Hundred to Subtract

### Lesson Purpose

The purpose of this lesson is for students to subtract 2 three-digit numbers using strategies based on place value.

### Lesson Narrative

In previous lessons, students subtracted 2 three-digit numbers and decomposed a ten or a hundred in order to subtract by place. Students analyzed problems to anticipate when one or more units may be decomposed and used their analysis to choose their method and their steps.

In this lesson, students subtract 2 three-digit numbers that require decomposing a hundred and a ten when subtracting by place. They connect the use of base-ten blocks or diagrams to written methods that use numbers and equations. Throughout the lesson, students interpret and share methods that use words and equations to show subtracting by place (MP2, MP7). However, students should be encouraged to attend to the numbers in expressions and may use base-ten blocks, base-ten diagrams, and any other representations that make sense to them.

• Engagement
• MLR8

### Learning Goals

Teacher Facing

• Subtract 2 three-digit numbers using place value strategies that include decomposing 2 units.

### Student Facing

• Let’s subtract within 1,000.

### Required Materials

Materials to Gather

Materials to Copy

• Walk About and Subtract Cards

### Required Preparation

Activity 2:

• Create a set of cards from the blackline master so that each student will receive 1 card.

### 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

What part of the lesson went really well today in terms of students learning? What did you do that made that part go well?

### Suggested Centers

• Target Numbers (1–5), Stage 5: Subtract Two-digit Numbers (Supporting)
• Number Puzzles: Addition and Subtraction (1–4), Stage 4: Within 100 with Composing (Supporting)

### Print Formatted Materials

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