Use a compass to draw a circle. Measure the diameter, and then draw a circle with a diameter that's twice as long as the first one.
Make a prediction: do you think the circumference of the larger circle is twice as long as the smaller circle? Why do you think that?
Test your predicition: Measure or calculate the circumference of each circle, and compare your results to your prediction.
Challenge: Use algebraic reasoning to show how the sizes of the two circumferences are related.
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