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 strategies and understandings students have for the relationship between addition and subtraction. Students who relate the pairs of equations are observing regularity in how addition and subtraction are related (MP8).
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 number that makes each equation true.
\(6 + \boxed{\phantom{\frac{aaai}{aaai}}} = 10\)
\(10 - 6 = \boxed{\phantom{\frac{aaai}{aaai}}}\)
\(8 +\boxed{\phantom{\frac{aaai}{aaai}}}= 10\)
\(10 - 2 =\boxed{\phantom{\frac{aaai}{aaai}}}\)
Student Response
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Activity Synthesis
“Who can restate _______ 's reasoning in a different way?”


aligns: no