Pi (π) Math Example 3

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Example 3

medium
A circular pool has a circumference of 31.4 m. Find its radius and area. Use π≈3.14\pi \approx 3.14.

Solution

  1. 1
    Step 1: Use the circumference formula C=2πrC = 2\pi r to find the radius: r=C2π=31.42(3.14)=31.46.28=5r = \frac{C}{2\pi} = \frac{31.4}{2(3.14)} = \frac{31.4}{6.28} = 5 m.
  2. 2
    Step 2: Apply the area formula: A=πr2=3.14×52=3.14×25=78.5A = \pi r^2 = 3.14 \times 5^2 = 3.14 \times 25 = 78.5 m².
  3. 3
    Step 3: State the results: radius =5= 5 m, area =78.5= 78.5 m².

Answer

r=5r = 5 m; A=78.5A = 78.5 m²
This problem chains two formulas together: first C=2πrC = 2\pi r solved for rr, then A=πr2A = \pi r^2. The circumference gives you the radius, and the radius gives you the area — showing how π\pi connects a circle's linear and area measurements.

About Pi (π)

The ratio of a circle's circumference to its diameter, approximately 3.14159…3.14159\ldots

Learn more about Pi (π) →

More Pi (π) Examples

Example 1 easy

A circle has a diameter of 10 cm. What is its circumference? Use [formula].

Example 2 medium

A circle has a radius of 7 m. Find its area. Use [formula].

Example 4 easy

A circle's circumference is [formula] cm. What is its diameter? Use [formula].

Example 5 hard

A wheel of radius 0.5 m rolls without slipping. How many full rotations does it make to travel 100 m

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