Grade 7 Math Book · Shapes & Geometry
Sir Cumference and the Dragon of Pi
by Cindy Neuschwander
After drinking a strange potion, Sir Cumference turns into a dragon. His son Radius has to find the cure, and it is hidden in a special number that links every circle's distance around to its distance across.
Why it's useful
A fun way to discover pi instead of just memorizing it.
- Circumference and diameter. Radius finds that the distance around is always a bit more than 3 times the distance across.
- Discovery, not rules. Students can measure real circles and find the same number.
- Memorable vocabulary. The character names keep circle words straight.
Try it in class or at home
- Measure circles. Use string to measure cans, plates and lids. Divide circumference by diameter.
- Class data. Put everyone's results in a table. What number keeps showing up?
- Use the formula. Predict the circumference of a new circle, then measure to check.