The purpose of this lesson is for students to compare methods for subtracting a one-digit number from a two-digit number with and without decomposing a ten.
In the first activity, students consider 3 methods for finding the difference represented using base-ten diagrams. In the second activity, students find the difference with and without decomposing a ten and represent their thinking using base-ten diagrams, words, or equations. Students are not expected to draw their work with base-ten diagrams in a specific way. Students should have access to base-ten blocks throughout the lesson and the cool-down. Students compare their methods, and the teacher records student thinking using base-ten diagrams and equations in the activity synthesis. In the lesson synthesis, students consider different ways to represent decomposing.
- Describe how methods of subtraction are the same and different when subtracting a one-digit number from a two-digit number.
- Let’s compare subtraction methods.
- Remove 0 and 10 from each set of cards (or prompt students to remove them) before the activity.
|Activity 1||15 min|
|Activity 2||20 min|
|Lesson Synthesis||10 min|
Teacher Reflection Questions
In upcoming lessons, students will subtract two-digit numbers from two-digit numbers with and without decomposing a ten. What do students need to understand about place value in order to use strategies that would require decomposing when subtracting by place?
- Capture Squares (1–3), Stage 3: Add within 20 (Addressing)
- Five in a Row: Addition and Subtraction (1–2), Stage 6: Add within 100 with Composing (Addressing)
Print Formatted Materials
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