standard_description: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
problem_activity: Narrative
The purpose of this activity is for students to build arrays with physical objects and describe the arrays in terms of multiplication. Students focus on where equal groups can be seen in arrays. Students will write expressions and equations to represent arrays in future lessons. In the activity, students are asked to create different arrays with 24 cubes. It is not an expectation of grade 3 for students to find all the arrays for a given number.
When students notice that the rows or columns in an array have the same number of objects and relate this to equal groups, they look for and make use of structure (MP7).
Keep connecting cubes out for the cool-down.
MLR8 Discussion Supports.
Synthesis:
Create a visual display of the various arrays created by the students. As students discuss each array, annotate the display with the language used, such as “array”, “rows”, “columns”, and “equal groups”.
Advances: Speaking, Representing
Representation: Internalize Comprehension.
Synthesis: Invite students to identify what is important or most useful to pay attention to. Display the sentence frame, “The next time I arrange objects in an array, I will remember to . . . .“
Supports accessibility for: Conceptual Processing, Visual-Spatial Processing, Memory
Required Materials
Materials to Gather
Connecting cubes
Required Preparation
Each group of 2 needs 60 cubes.
Launch
Groups of 2
Give each group of 2 students at least 60 connecting cubes.
Activity
7–10 minutes: partner work time
Monitor for students who relate the same number of objects in each row and column in an array to how multiplication expresses equal groups of objects.
Student Facing
Use cubes to make 6 groups of 5.
Arrange them into an array.
Explain or show how the array is related to equal groups.
Count out 20 cubes.
Arrange them into as many arrays as you can.
Explain or show how each array is related to equal groups.
Count out 24 cubes.
Arrange them into as many arrays as you can.
Explain or show how each array is related to equal groups.
Student Response
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Activity Synthesis
Have students share different arrays they made for the last problem.
“Why were you able to create different arrays with 24 objects?” (There are many ways to put 24 things into equal groups.)


aligns: no