Unit 8, Lesson 9
A Sum of Equal Addends
Grade 2
Preparation
Lesson Narrative
In this lesson, students match expressions with equal addends to arrays and find the total number of objects in an array by finding the value of these sums. The primary focus of the lesson is on relating sums with equal addends to the structure of the rows and columns in an array in order to build foundations for using arrays to represent multiplication in grade 3.
The arrays in the lesson also invite students to decompose the array in ways that make sense to them. It is important to recognize other ways students may use expressions to represent arrays.
For example, students might find the total number of counters in a 3-by-4 array by adding . Although this expression does not directly match the structure of the rows and columns, it would be important to invite students to share why they chose this expression and how they may have used the rows or columns.
When students compare the expression to the sum of the number of counters in each column () or the sum of the counters in each row (), it helps build conceptual foundations for multiplication and the properties of operations that will be explored in future grades.
For arrays that don’t have the same number of rows as columns, there are 2 addition expressions that can represent the number of objects in the array.
- Representation
- MLR2
- Explain (orally) strategies for finding the total number of objects in an array.
- Match (orally) expressions with equal addends and arrays that represent the same value.
- Let’s match expressions with arrays.
Required Preparation
- Create a set of cards for each group of 2–3.
Teacher Reflection Questions
As students worked in their small groups today, whose ideas were heard, valued, and accepted? How can you adjust the group structure tomorrow to ensure each student’s ideas are a part of the collective learning?