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 Number Talk is to elicit understandings students have for adding and subtracting within 20 using the strategy of making a ten.
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.
\(10 + 4\)
\(9 + 4\)
\(9 + 6\)
\(15 – 6\)
Student Response
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Activity Synthesis
“Did anyone approach the problem in a different way?”


aligns: no