Unit 1, Lesson 19
Solve Problems Involving Arrays
Grade 3
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The purpose of this Number Talk is to elicit strategies and understandings students have about equal groups in multiplication expressions and to see a pattern as one factor is decreased. These understandings help students develop fluency and will be helpful later in this lesson when students will need to use multiplication to answer questions about array situations.
When students notice that the product decreases by a group of 2 as the number being multiplied by 2 decreases by 1, they look for and express regularity in repeated reasoning (MP8).
Find the value of each expression mentally.
None
The purpose of this activity is for students to write an equation with a symbol for the unknown to represent an array situation. Then they answer the question about the situation. Encourage students to use whatever strategy or representation feels appropriate to them. Given their prior experiences, they might represent the situation with an array and skip-count or consider equal groups in other ways to find the total.
In the Launch, it may be helpful to ask students to tell their partner a quick story or ask any questions about the context of the first problem. To ensure all students have access, it may also be helpful to display images for students to reference about coconut trees or Mexico.
For each problem:
A field of coconut trees in Mexico has 5 rows of trees. Each row has 9 trees. How many trees are there?
Tyler wants to plant coconut trees in a community garden in Florida. He will plant 2 rows of 4 trees. How many trees will Tyler plant?
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