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 True or False is to elicit insights students have about numbers being represented in different ways. The reasoning students do here deepens their understanding of how numbers can be composed and decomposed in different ways using tens and ones.
Launch
Display one statement.
“Give me a signal when you know whether the statement is true and can explain how you know.”
1 minute: quiet think time
Activity
Share and record answers and strategy.
Repeat with each statement.
Student Facing
Decide if each statement is true or false.
Be prepared to explain your reasoning.
\(92 = 90 + 2\)
\(90 + 2 > 80 + 12\)
\(20 + 13 < 30 + 13\)
Student Response
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Activity Synthesis
“How can you determine whether each is true or false without finding the value of each side?”
If needed, ask “How can you use what you know about tens and ones to help you know if it is true or false?” (I can compare the number of tens first, then compare ones.)


aligns: no