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 Choral Count is for students to practice counting back by 10 and notice patterns in the count. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to decompose hundreds.
Launch
“Count back by 10, starting at 590.”
Record as students count.
Stop counting and recording at 390.
Activity
“What patterns do you see?”
1–2 minutes: quiet think time
Record responses.
Student Response
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Activity Synthesis
“What comes after 390 if we keep counting back by 10? What comes after 300?”


aligns: no