standard_description: Prove that, given a system of two equations in two variables, replacing one equation by the sum of that equation and a multiple of the other produces a system with the same solutions.
problem_activity: Warm-up
The purpose of this Math Talk is to elicit strategies and understandings students have for multiplying by 1.5 and adding to another value. These understandings help students develop fluency and will be helpful later when students will need to be able to compute the cut-off values for outliers.
Launch
Display one problem at a time. Give students quiet think time for each problem and ask them to give a signal when they have an answer and a strategy. Keep all problems displayed throughout the talk. Follow with a whole-class discussion.
Student Facing
Solve each expression mentally.
\(20 + 1.5(10)\)
\(20 - 1.5(10)\)
\(20 + 1.5(14)\)
\(20 + 1.5(13)\)
Student Response
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Activity Synthesis
Ask students to share their strategies for each problem. Record and display their responses for all to see. To involve more students in the conversation, consider asking:
“Who can restate
\(\underline{\hspace{.5in}}\)
’s reasoning in a different way?”
“Did anyone have the same strategy but would explain it differently?”
“Did anyone solve the problem in a different way?”
“Does anyone want to add on to
\(\underline{\hspace{.5in}}\)
’s strategy?”
“Do you agree or disagree? Why?”


aligns: no