Circle of radius 20 cm: its circumference

A circle has a radius of 20 cm. Find the circumference of this circle.

Step-by-step

1. 2 × π × 20 = 125.66
   Circumference = 2πr

Why it works

The circumference of a circle is its diameter times pi, and the diameter is twice the radius.

Common mistakes

• Treating the radius 20 cm as if it were the diameter.
• Using 3.14 × 20 × 20, which is the area formula.

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