In this page we practice using the relationship between the circumference and diameter of a circle.
We also practice:
- approximating \(\pi\)
- finding circumference
- comparing straight and curved distances
- using circle formulas
Example 1 – Find the Circumference
A circle has diameter:
\(D=10 \text{ cm}\)
Using:
\(C=\pi D\)
and approximating:
\(\pi \approx 3.14\)
we get:
\(C \approx 3.14×10\)
\(C \approx 31.4 \text{ cm}\)
Example 2 – Another Circumference
A circle has diameter:
\(D=20 \text{ m}\)
Using:
\(C = \pi D\)
\(C \approx 3.14×20\)
\(C \approx 62.8 \text{ m}\)
Example 3 – Semicircle Distance
A circle has circumference:
\(C=50 \text{ m}\)
Find the distance around half of the circle.
\(\frac{1}{2}C=\frac{1}{2}(50)=25 \text{ m}\)
So, the semicircle distance is:
\(25 \text{ m}\)
Example 4 – Estimate Using \(\pi \approx 3\)
A circle has diameter:
\(D=40 \text{ m}\)
Using:
\(\pi \approx 3\)
we get:
\(C \approx 3×40=120 \text{ m}\)
Example 5 – Compare Distances
A circular path has diameter:
\(D=100 \text{ m}\)
Direct distance across:
\(100 \text{ m}\)
Upper curved path:
\(\frac{1}{2} \pi D\)
Using:
\(\pi \approx 3\)
\(\frac{1}{2}(3)(100)=150 \text{ m}\)
So the curved path is longer.
Practice
- More Examples (Current page)
- Take the Quiz
Continue Learning
- What is \(\pi\) (pi)? An Easy Explanation
- Why the Area of a Circle is \(\pi r^2\) (Visual Explanation)