Smart Math guide · Geometry Smarts

Estimate Circles Before Using π

Use π≈3.14 or π≈22/7 when suitable, but first judge whether radius or diameter is being used.

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The method

How to use it

  1. Identify radius r and diameter d=2r.
  2. Circumference C=2πr; area A=πr².
  3. Estimate scale before precise calculation.
Worked example

See it in action

r=5: circumference≈31.4, area≈78.5.

Check your thinking

How to verify it

Area should be under the 10×10 bounding square of area 100.

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