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 to invite students to practice counting by 1 beyond 120 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 use centimeters and meters to record lengths. For example, some students may record 1 meter and 30 centimeters as 130 centimeters.
Students may wonder about the place value of three-digit numbers. Although students are not expected to understand the hundreds place yet, be prepared to say that the 1 means 1 hundred without going too far. Unitizing 100 will be addressed in a later unit.
Launch
“Count by 1, starting at 20.”
Record as students count.
Stop counting and recording at 30.
“Count by 1, starting at 120.”
Record as students count directly below the first count.
Stop counting and recording at 130.
Activity
“What patterns do you see?”
1–2 minutes: quiet think time
Record responses.
Student Response
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Activity Synthesis
“Who can restate the pattern in different words?”
“Does anyone want to add an observation on why that pattern is happening here?”
“Do you agree or disagree? Why?”


aligns: no