standard_description: Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for multiplying a one-digit number and a two-digit number, which will be helpful later in this lesson when students continue to practice multiplying 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.
\(4\times10\)
\(4\times20\)
\(4\times21\)
\(4\times24\)
Student Response
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Activity Synthesis
“How did you figure out the more challenging products?” (Once I knew
\(4\times20\)
, I was able to build on it to find
\(4\times21\)
and
\(4\times24\)
by just adding more fours. I knew that 4 groups of 25 make 100, so I took away 4 to find 4 groups of 24.)


aligns: no