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The shrink ray problem

7th GradePercent changeabout 2 minCCSS 7.RP.A.3

Guess which grow ray gets you back, then try your own shrink.

Lesson Plan

Practice percent increase and decrease, including the percent needed to return to a starting value.

  1. Question: Ask what students spot and what they are curious about. Read “Which grow ray gets you back?” aloud. Have each student guess and say why.

  2. Big idea: Pause. Ask a student to say the idea in their own words.

  3. Question: Read “How much must it grow back?” aloud. Have partners explain their guesses to each other.

  4. Real-world application: Ask: Where else have you seen this?

  5. Your turn: Have students try their own. Ask them to predict before they test.

How to run it

  1. Whole classPut the lesson on the board. At each choice the class votes, then you select the winner.
  2. SoloShare the link, QR code, or post to Google Classroom. Each student gets to take their own path.