standard_description: Fluently add and subtract within 20 using mental strategies. (See standard 1.OA.6 for a list of mental strategies.) By end of Grade 2, know from memory all sums of two one-digit numbers.
problem_activity: Narrative
The purpose of this activity is for students to choose methods flexibly for finding the value of differences. Students might subtract by place, count on, or make an easier problem. There is no right answer to which method should be used for each problem. Students should choose a method that makes sense to them and justify their choice (MP3).
Engagement: Provide Access by Recruiting Interest.
Provide choice. Invite students to decide the order of the problems to complete the task. They can choose to work through in any order.
Supports accessibility for: Social-Emotional Functioning, Organization
Required Materials
Materials to Gather
Base-ten blocks
Launch
Groups of 2
Give students access to base-ten blocks.
“We’ve learned how to decompose units to subtract by place and different ways to represent that. We’ve also learned other methods for subtracting. We use them when they make sense to us or when they make sense for the numbers in an expression.”
Activity
“Find the value of each expression using a method that makes sense to you. You’ll have a chance to share your work with others.”
6 minutes: independent work time
Monitor for expressions that most students find the same way and expressions that many students find in different ways.
“Find a partner who found the value of _____ the same way as you.”
1–2 minutes: partner discussion
“Now find a partner that found the value of _____ in a different way than you. Share your thinking.”
2–3 minutes: partner discussion
Repeat for additional expressions as desired.
Student Facing
Find the value of each expression in a way that makes sense to you. Show your thinking. Organize it so it can be followed by others.
\(535 - 214\)
\(700 - 589\)
\(683 - 398\)
\(918 - 608\)
\(735 - 457\)
\(602 - 487\)
Student Response
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Advancing Student Thinking
If students use the same method for each problem, ask students to think about how they could use Jada’s way to find the value of
\(701 - 599\)
. Consider asking:
“What do you notice about the numbers in this expression that makes it easier to use Jada’s way?”
“What other expressions do you see where you might try Jada’s way?”
Activity Synthesis
Have 3–4 students share a method or representation that someone they talked to shared.
“What methods or representations do you want to try more?”


aligns: no