Subtraction Algorithms (Part 3)
The purpose of this lesson is for students to use a subtraction algorithm that records a single digit for the difference between the numbers in each place value position and a condensed notation for a decomposed hundred or ten.
In this lesson, students continue to learn how to use algorithms to subtract within 1,000. The new algorithm in this lesson draws attention to how place value can be used to record less digits in each place value position. This condensed notation also changes the steps of the algorithm because students don't write the numbers in expanded form to start or add up the partial differences at the end.
Activity 1: A New Subtraction Algorithm
- Relate subtraction algorithms to one another using place value understanding.
- Subtract numbers within 1,000 using another algorithm based on place value.
- Let’s learn another algorithm to subtract.
Materials to Gather
|Activity 1||20 min|
|Activity 2||15 min|
|Lesson Synthesis||10 min|
Teacher Reflection Questions
Who got to do math today in class and how do you know? Identify the norms or routines that allowed these students to engage in mathematics. How can you adjust these norms and routines so all students do math tomorrow?
- 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)