standard_description: Prove theorems about triangles. Theorems include: a line parallel to one side of a triangle divides the other two proportionally, and conversely; the Pythagorean Theorem proved using triangle similarity.
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for adding more than 2 two-digit numbers by making 100. The unit of cents also encourages students to consider how the value could be expressed using dollars, cents, or a combination of the two units. These understandings help students develop fluency.
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 strategies.
Keep expressions and work displayed.
Repeat with each expression.
Student Facing
Find the value of each expression mentally.
\(80¢ + 20¢ + 37¢\)
\(80¢ + 20¢+ 37¢+ 42¢\)
\(75¢ + 37¢ + 25¢\)
\(75¢ + 80¢ + 25¢ + 20¢\)
Student Response
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Activity Synthesis
Revisit a student strategy that shows looking for a way to make 100 first and expresses the total in cents.
Consider asking:
“Who can restate _____'s reasoning in a different way?”
“Who can restate _____'s reasoning using dollars and cents?”


aligns: no