standard_description: Classify objects into given categories; count the numbers of objects in each category and sort the categories by count. (Limit category counts to be less than or equal to 10.)
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for subtracting within 1,000, particularly around adding up to find differences. These understandings help students develop fluency for subtracting within 1,000.
Launch
Display one expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Activity
Record answers and strategy.
Keep expressions and work displayed.
Repeat with each expression.
Student Facing
Find the value of each expression mentally.
\(500 - 475\)
\(504 - 475\)
\(512 - 475\)
\(512 - 449\)
Student Response
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Activity Synthesis
”Why is the value of
\(512 - 475\)
greater than the value of
\(504 - 475\)
?” (Since the 475 doesn’t change, but 512 is larger than 504, the difference between the numbers is greater.)
Consider asking:
“Who can restate _____’s reasoning in a different way?”
“Did anyone have the same strategy but would explain it differently?”
“Did anyone approach the problem in a different way?”
“Does anyone want to add on to _____’s strategy?”


aligns: no