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Grade 2 · lesson 4 of 4

Use a Small Symbol Code

Translate symbols with a supplied code key and preserve their order.

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Supplied materials

  • Paper and pencil; an adult may read aloud. No device, account or purchase is needed.

Learn the idea

A code key gives symbols an agreed meaning. This lesson’s key is A = circle and B = triangle. These letter codes are invented for this exercise; they are not a standard computer text code. Decoding means replacing each code symbol with the shape named in the key.

The message A B B A has four positions. Decode one position at a time, without sorting the letters. A repeated letter still stands for a shape each time it appears. You can check your decoded picture by encoding the shapes back into letters and comparing them with the starting message.

  1. Write the two-entry key A = circle, B = triangle.
  2. Write message A B B A with a box around each letter.
  3. Replace each letter with its shape in the same position.
  4. Encode your output back into letters to check all four positions.
Worked example

See the method in action

A B B A decodes to circle, triangle, triangle, circle. Encoding that shape sequence returns A B B A, so both the symbols and their order are preserved.

Your turn

Check your reasoning

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Using the same key, what does B A B mean?

Feedback appears here after you check. This is practice, not a graded school assessment.

See the answer and explanation

Triangle, circle, triangle

B maps to triangle and A maps to circle. Applying the key in order gives triangle, circle, triangle.

Take it further

Add C = square to the key and decode C A B C. Expected output: square, circle, triangle, square. Encoding it back returns C A B C.

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Check the subject sources

These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.