Circumference — Grade 7 Accelerated, what it means and where it is taught
The perimeter of a circle: C = 2π r.
Taught in Grade 7 Accelerated.
Where it is taught
What it rests on
Work through these first if this one does not settle.
- Perimeter — Distance all the way around the outside.
What uses it later
This idea is needed for:
- π — The circumference of any circle divided by its diameter — about 3.14159.
Practise this idea
7 questions in the course bank use Circumference, in Length and Area in 2-D Figures, Circles.
Problem 1
Find the circumference of a circle with radius 3. Use π ≈ 3.14.
Worked answer
18.84
2 × 3.14 × 3 = 18.84
Problem 2
A circle has circumference 31.4. Find its radius. Use π ≈ 3.14.
Worked answer
5
31.4 = 6.28r
r = 31.4 ÷ 6.28 = 5
Problem 3
Find the circumference of a circle with radius 5. Use π ≈ 3.14.
Worked answer
31.4
2 × 3.14 × 5 = 31.4
Problem 4
Find the circumference of a circle with radius 7. Use π ≈ 227.
Worked answer
44
2 × 227 × 7 = 44
Problem 5
A circle has circumference 62.8. Find its radius. Use π ≈ 3.14.
Worked answer
10
62.8 = 6.28r
r = 10
Problem 6
Find the arc length of a quarter circle of radius 8, in terms of π (enter just the number in front of π).
Worked answer
4
Full circumference: 16π
A quarter: 4π
Problem 7
Find the arc length of a 90° sector of a circle with radius 10. Use π ≈ 3.14.
Worked answer
15.7
Full circumference: 2 × 3.14 × 10 = 62.8
14 × 62.8 = 15.7