standard_description: Use the structure of an expression to identify ways to rewrite it. For example, see x^(4) – y^(4 )as (x^(2))^(2 )– (y^(2))^(2), thus recognizing it as a difference of squares that can be factored as (x^(2 )– y^(2))(x^(2 )+ y^(2)).
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for dividing within 100. These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to divide fluently within 100.
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.
\(5 \times 5\)
\(10 \times 5\)
\(2 \times 5\)
\(85 \div 5\)
Student Response
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Activity Synthesis
“How did knowing the first 3 facts help you find the value of
\(85 \div 5\)
?” (The first 3 products added up to 85, which was the number I was dividing in the last problem. So, I was able to use those to figure out
\(85 \div 5\)
.)


aligns: no