standard_description: Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have about the relationship between addition and subtraction. Each addition and subtraction equation represents the same part-whole relationship. These understandings help students develop fluency and will be helpful later in this lesson when students solve missing addend problems.
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 missing value mentally.
\(4 + \boxed{\phantom{1}} = 5\)
\(5 - \boxed{\phantom{1}} = 4\)
\(6 + \boxed{\phantom{2}} = 8\)
\(8 - \boxed{\phantom{2}} = 6\)
Student Response
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Activity Synthesis
“How can finding the missing value in the first equation help you with the second equation?" (I know that 1 more than 4 is 5, so I also know that 1 less than 5 is 4.)


aligns: no