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: Narrative
This warm-up prompts students to carefully analyze and compare different arrays. The activity also enables the teacher to hear how they talk about arrays, rows, and columns, and how they find the total number of objects in an array.
Launch
Groups of 2
Display the image.
“Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
1 minute: quiet think time
Activity
“Discuss your thinking with your partner.”
2–3 minutes: partner discussion
Record responses.
Student Facing
Which one doesn’t belong?
A
[IMG]
B
[IMG]
C
[IMG]
D
[IMG]
Student Response
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Activity Synthesis
“What do B, C, and D have in common?” (They all show arrays with 3 in each row.)
“D has 4 rows and 3 columns. This rectangle is partitioned into equal-size squares.”


aligns: no