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Grade 4 · unit review

Review: Encode Pictures and Written Messages

Represent a 2×3 picture with paletteA=dark,B=light and row sequencesABA/BAB. Count pixels and estimate its data at 2 bytes per pixel; state the model’s limit.

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Unit review questions
1. A paper pixel image has 4 rows and 8 columns. How many pixel positions need values?
Need a hint?
  • Multiply the number of rows by the number of columns to count pixel positions.
  • The count of positions is not automatically the file size in bytes.
2. Row AAB. Palette: A=dark, B=light. Decode the three-pixel row.
Need a hint?
  • Use the explicit input, condition and question aspect.
  • Reject a choice that adds an unsupported condition or answers a different question.
3. Sequence 2,3. Code: 1=A, 2=B, 3=C. Decode the supplied sequence.
Need a hint?
  • Use the explicit input, condition and question aspect.
  • Reject a choice that adds an unsupported condition or answers a different question.
4. The model stores 24 pixels at 2 bytes per pixel, with no other data. How many bytes?
Need a hint?
  • Multiply recorded element count by the stated bytes per element, using consistent units.
  • An uncompressed classroom estimate is not an exact real file size.

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Use the skills in a new task

Represent a 2×3 picture with paletteA=dark,B=light and row sequencesABA/BAB. Count pixels and estimate its data at 2 bytes per pixel; state the model’s limit.

Work on paper or in your own document. Explain the choices you made.

  • Use the pretend details in the task and name the rule you followed.
  • Show the steps or point to the detail that helped you choose.
  • Say one mistake to avoid or one thing this example cannot tell us.
  • Check your answer against the task. Change a part if you can show why it needs fixing.
Compare with a model response

Two rows times three columns give 6 pixels. The palette decodes dark-light-dark/light-dark-light. At 2 bytes each, data is 12 bytes in this no-overhead model; a real file may include metadata or compression.

A different response can also meet the criteria. Compare the evidence and reasoning, rather than copying the wording.