standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Narrative
The purpose of this activity is for students to add 2 two-digit numbers within 100 and show their thinking with equations. Although some students may write each step of their thinking with equations, it is not required that they do so. Students can write one equation that shows the sum and represent their solution pathway in their drawings. In the activity synthesis, students present their method verbally to a new partner.
This activity uses
MLR8 Discussion Supports. Advances: listening, speaking, conversing
Required Materials
Materials to Gather
Connecting cubes in towers of 10 and singles
Launch
Groups of 2
Give students access to connecting cubes in towers of 10 and singles.
“We have been learning about different ways to add within 100. You are going to find sums using a method that makes most sense to you for each problem. Record equations to show your thinking.”
Activity
5 minutes: independent work time
“Compare your work with your partner’s. Did you use the same method? Did you represent your method in the same way? How is your work the same? How is it different?"
5 minutes: partner work time
Monitor for a student who wrote equations related to making ten and one who wrote equations related to adding by place.
Student Facing
Find the value of each sum using any method that you want.
Show your thinking using drawings, numbers, or words.
Write equations to represent your thinking.
\(48 + 15\)
\(57 + 36\)
Student Response
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Activity Synthesis
MLR8 Discussion Supports:
Display sentence frames to support students when they explain their method as equations:
“First, I _____ because . . .”
“I noticed _____ so I . . .”
“You are going to explain your method to another student in the class. Practice what you will say with your partner. Use these sentence starters to help you.”
3 minutes: partner discussion
“Find a new partner and explain your method.”
2 minutes: partner discussion


aligns: no