Case Study

In the model for x+3=8x+3=8, what do the envelope, a counter, and the center line represent?

Case context: An envelope and three counters are on the left. Eight counters are on the right.

Question: In the model for x+3=8x+3=8, what do the envelope, a counter, and the center line represent?

Sample answer: The envelope represents the unknown variable xx. A counter represents a known number, or constant. The center line represents the equal sign ==.

Key points:

  • Envelope: variable or unknown xx
  • Counter: constant or known number
  • Center line: equal sign ==

Rubric: Full credit: Correctly identifies all three parts. Partial credit: Correctly identifies one or two parts.

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Updated 2026-08-12

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