Unit 2, Lesson 2
Find the Unknown Addend
Grade 2
Preparation
Lesson Purpose
The purpose of this lesson is for students to find the value of unknown addends by adding or subtracting within 100.
Lesson Narrative
In a previous lesson, students added and subtracted within 100 without composing or decomposing a ten to solve Compare problems. In this lesson, students add or subtract within 100 without composing or decomposing a ten and share the ways they find unknown addends. During each Synthesis, students share approaches based on place value and discuss the relationship between addition and subtraction.
This lesson also serves the purpose of introducing base-ten blocks as a math tool that can be used to represent greater numbers and computation methods based on place value. Throughout the lesson, students have opportunities to describe the usefulness of this new tool in comparison to connecting cubes and other representations they may use to find unknown values (MP5).
- Engagement
- MLR8
- Explain (orally) representations and strategies used to find an unknown addend, including those based on place value.
- Let’s find values that make the equations true.
Required Materials
Activity 1
Activity 2
Required Preparation
Activity 1
- Each group of 2 needs 90–100 connecting cubes, but no more than 3–5 towers of 10 cubes should be included in their collection. Break apart any extra towers for this activity.
Teacher Reflection Questions
Who did math today in class and how do you know? Identify the norms or routines that allowed those students to engage in mathematics. How can you adjust these norms and routines so all students do math tomorrow?
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