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:
\(D=10 cm\)
Using:
\(C=πD\)
and approximating:
\(\pi \approx 3.14\)
we get:
\(C \approx 3.14×10\)
\(C \approx 31.4 cm\)
Example 2 – Another Circumference
A circle has diameter:
\(D=20 m\)
Using:
\(C=πD\)
\(C \approx 3.14×20\)
\(C \approx 62.8 m\)
Example 3 – Semicircle Distance
A circle has circumference:
\(C=50 m\)
Find the distance around half of the circle.
\(\frac{1}{2}C=\frac{1}{2}(50)=25 m\)
So, the semicircle distance is:
\(25 m\)
Example 4 – Estimate Using \(\pi \approx 3\)
A circle has diameter:
\(D=40 m\)
Using:
\(\pi \approx 3\)
we get:
\(C \approx 3×40=120 m\)
Example 5 – Compare Distances
A circular path has diameter:
\(D=100 m\)
Direct distance across:
\(100 m\)
Upper curved path:
\(\frac{1}{2} πD\)
Using:
\(\pi \approx 3\)
\(\frac{1}{2}(3)(100)=150 m\)
So the curved path is longer.
Practice
- More Examples
- Take the Quiz