Worked example
A circle has radius 2 cm. What is its exact circumference?
Answer & why
Answer: 4π cm
The diameter is 2 × 2 = 4 cm. Circumference is π times diameter, so C = 4π cm.
Grade 7 · Math
Find a circle’s exact circumference
Connect circumference, diameter and radius with C = πd = 2πr.
6 authored questions + worked example
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All questions
All 6 authored questions for this skill.
Question 1
A circle has radius 4 cm. What is its exact circumference?
- 16π cm
- 8π cm
- 4π cm
- 8 cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 8π cm
The diameter is 2 × 4 = 8 cm. Circumference is π times diameter, so C = 8π cm.
Question 2
A circle has radius 5 cm. What is its exact circumference?
- 20π cm
- 10 cm
- 10π cm
- 5π cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 10π cm
The diameter is 2 × 5 = 10 cm. Circumference is π times diameter, so C = 10π cm.
Question 3
A circle has radius 6 cm. What is its exact circumference?
- 12π cm
- 6π cm
- 12 cm
- 24π cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 12π cm
The diameter is 2 × 6 = 12 cm. Circumference is π times diameter, so C = 12π cm.
Question 4
A circle has radius 7 cm. What is its exact circumference?
- 28π cm
- 14π cm
- 14 cm
- 7π cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 14π cm
The diameter is 2 × 7 = 14 cm. Circumference is π times diameter, so C = 14π cm.
Question 5
A circle has radius 2 cm. What is its exact circumference?
- 2π cm
- 4π cm
- 8π cm
- 4 cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 4π cm
The diameter is 2 × 2 = 4 cm. Circumference is π times diameter, so C = 4π cm.
Question 6
A circle has radius 3 cm. What is its exact circumference?
- 6π cm
- 12π cm
- 6 cm
- 3π cm
A hint
Circumference is the boundary length. Use C = 2πr and keep π for an exact answer.
Answer & why
Answer: 6π cm
The diameter is 2 × 3 = 6 cm. Circumference is π times diameter, so C = 6π cm.