Different Ways to Decompose
In previous lessons, students used their own methods for subtracting a two-digit number from a two-digit number. In this lesson, students make sense of different subtraction methods that use base-ten drawings to represent decomposing a ten to subtract by place. Students connect base-ten drawings to equations that represent the steps of a subtraction method. Throughout the lesson, students share claims and justify how methods are the same and how they are different with an emphasis on describing how tens are subtracted from tens and ones from ones and deepening their understanding of the properties of operations (MP3, MP7).
Students should have access to base-ten blocks throughout the lesson and cool-down as they make sense of and try different methods and representations.
- Describe how methods of subtraction are the same and different when subtracting a one-digit number from a two-digit number.
- Let’s compare different ways to subtract.
Materials to Gather
|Activity 1||15 min|
|Activity 2||20 min|
|Lesson Synthesis||10 min|
Teacher Reflection Questions
- 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)
- Target Numbers (1–5), Stage 4: Subtract Tens or Ones (Addressing)