Lesson 9
Subtraction Algorithms (Part 2)
Lesson Purpose
The purpose of this lesson is for students to subtract within 1,000 using a subtraction algorithm that records numbers in expanded form.
Lesson Narrative
Previously, students learned to record subtraction using an algorithm in which the numbers are written in expanded form. They made connections between the structure and steps of the algorithm to those of base-ten diagrams that represent the same subtraction. In this lesson, students take a closer look at the algorithm and use it to find differences. They also examine a common error in subtracting numbers when decomposition of a place value unit is required. When students discuss shown work, they construct viable arguments and critique the reasoning of others (MP3).
- Engagement
- MLR8
Learning Goals
Teacher Facing
- Analyze and use a subtraction algorithm with the numbers written in expanded form.
Student Facing
- Let’s learn more about our first subtraction algorithm.
Required Materials
Materials to Gather
Required Preparation
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
Today students were able to analyze a common error when subtracting within 1,000 before they used an algorithm to subtract. How did the analysis of the error affect their work with subtracting within 1,000?
Suggested Centers
- How Close? (1–5), Stage 4: Add to 1,000 (Addressing)
- Number Puzzles: Addition and Subtraction (1–4), Stage 5: Within 1,000 (Addressing)
- Five in a Row: Multiplication (3–5), Stage 2: Factors 1–9 (Supporting)