standard_description: Fluently add and subtract within 20 using mental strategies. (See standard 1.OA.6 for a list of mental strategies.) By end of Grade 2, know from memory all sums of two one-digit numbers.
problem_activity: Narrative
This Number Talk encourages students to think about the relationship between addition and subtraction to mentally solve problems. This builds on the work in the previous lesson where students used the relationship between addition and subtraction to find unknown numbers in equations. The understanding elicited here will be helpful later in the lesson when students find the value to make an equation true.
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.
\(7+3\)
\(10-7\)
\(10-2\)
\(10-4\)
Student Response
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Activity Synthesis
“How did thinking about addition help you subtract?” (I thought about what number I could add to the 4 to make 10. Since I know 4 + 6 = 10 then I knew 10 – 4 = 6)
If needed, use connecting cubes to represent students’ thinking.


aligns: yes