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Estimate Pi

Posted by Angie Seltzer on 3/13/2016 to 6-8 Geometry
Estimate Pi
Explain to students that pi is the distance around the circle that is one unit across. It's easy to estimate pi by comparing to the distance around a square or hexagon. Draw sketches such as the ones below with labels only on each diameter.
Circle Inscribed in SquareHexagon Inscribed in Circle
Ask students these questions and mark the lengths as students respond.
  • What is the length of each side of the square? [1 unit]
  • If the diameter of the circle is one unit, what is the distance around the square? [4 units]
  • What is the length of each side of the hexagon? [1/2 unit]
  • What is the total distance around the hexagon? [3 units]
  • Is the distance around the circle closer to 3 or 4? [Closer to 3]
These diagrams and questions should help students remember that pi is a little greater than 3. Explain that the rounded value is 3.14 but the exact value is an irrational number. Happy Pi Day!