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 use what they know about the base-ten structure of numbers to create different expressions. Students use place value reasoning to create expressions with the smallest and largest values and expressions that may or may not require composing a ten when adding using methods based on place value (MP7). In the synthesis, students explain how they reasoned about whether or not a new ten could be composed just by looking at the addends (MP3). Although some students may complete the activity without finding any sums, others may need to find partial sums or complete sums in order to explain what happens when adding.
MLR8 Discussion Supports.
Synthesis: For each method that is shared, invite students to turn to a partner and restate what they heard using precise mathematical language.
Advances: Listening, Speaking
Representation: Access for Perception.
Some students may benefit from hearing the instructions read aloud more than once.
Supports accessibility for: Attention, Language, Memory
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.
“Now we are going to use what we know about numbers and addition to think about what will happen when we add different numbers together. You may add the numbers if it is helpful, but you don’t have to.”
Activity
8 minutes: partner work time
Monitor for students who write expressions without finding the value of the sums and can explain their reasoning.
Student Facing
37
22
18
56
41
Choose 2 numbers from above and write an addition expression to make each statement true.
This sum has the smallest possible value.
Expression:_______________________
This sum has the largest possible value.
Expression:_______________________
You do not need to make a new ten to find the value of this sum.
Expression:_______________________
If you make a new ten to find the value of this sum, you will still have some more ones.
Expression:_______________________
If you make a new ten to find the value of this sum, you will have no more ones.
Expression:_______________________
Be ready to explain your thinking in a way that others will understand.
If you have time: Choose 2 numbers from above and write an addition expression where the value is closest to 95.
How do you know the value is closest to 95?
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Student Response
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Activity Synthesis
Invite a previously identified student to share their expression that does not require making a new ten.
“Are there other numbers you could use? How do you know?"
Invite a student who found two numbers that make a ten without finding the sums to share.
“Are there other numbers you could use? How do you know?"


aligns: no