standard_description: Mentally add 10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number 100–900.
problem_activity: Narrative
The purpose of this activity is for students to compose and decompose numbers 11–19 as 10 ones and some more ones. Students work with groups of 11–19 objects to represent a context about students in a classroom where there is room for 10 students to sit at a table and the rest of the students sit on a rug. To solve the problem, students may count the total number of objects and then find a group of 10 or they may start by putting 10 objects at the table and see how many cubes are left on the rug and count all, count on, or know the total without counting. They record the two groups and the total by filling in equations.
Students work with multiple collections of 11–19 objects. They can be given access to a variety of collections of objects to choose from and then switch collections with other groups.
MLR8 Discussion Supports.
Invite students to act out the scenario. Listen for and clarify any questions about the context.
Advances: Speaking, Representing
Action and Expression. Develop Expression and Communication:
Give students access to 10-frames to help them figure out the number of students that will be sitting at the table and rug.
Supports accessibility for: Conceptual Processing, Visual-Spatial Processing
Required Materials
Materials to Gather
Collections of objects
Required Preparation
Each group of 2 needs access to at least 2 collections of 11–19 objects.
Launch
Groups of 2
Give each group of students access to collections of 11–19 objects.
“We are going to pretend that the objects in the collection are students.”
“The students will either sit at the table or on the rug.”
Display the image.
“All of the students want to sit at the table. How many of the students can sit at the table?” (10 students)
1 minute: independent work time
“10 students can sit at the table. The students who do not fit at the table will sit on the rug.”
“Work with your partner to figure out how many students will sit at the table, how many will sit on the rug, and how many students there are altogether. Fill in an equation for each bag of objects.”
Activity
7 minutes: partner work time
Student Facing
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Student Response
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Activity Synthesis
“The collection Jada is working with has 14 objects. She showed 10 students sitting at the table. How many do you think will be still on the rug? Why do you think that?” (4, 10 and 4 is 14)


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