8th Grade Circumference and Area of Circles Worksheet — Level 3 — Practice Set 3 — Answers
Answer sheet with worked solutions for the 8th Grade area & perimeter worksheet.
Success TutoringWorksheetsAnswer sheet8th Grade · Mathematics · Area & Perimeter8th Grade Circumference and Area of Circles Worksheet — Level 3 — Practice Set 3 — Answers
Show your work. Use the π button on your calculator and round to 1 decimal place unless told otherwise.
1.A circle has a circumference of 40π cm. Find its radius and its area (leave the area in terms of π).
Answer: r = 20 cm; A = 400π cm2
- C = 2πr, so 2πr = 40π
- r = 20 cm
- A = πr2 = 400π cm2
2.A circle has a diameter of 4 cm. Find its area, correct to 1 decimal place.
Answer: 12.6 cm2
- r = 4 ÷ 2 = 2 cm
- A = π × r2 = π × 22 = π × 4
- ≈ 12.6 cm2
3.Find the area of a semicircle with a radius of 16 cm, correct to 1 decimal place.
Answer: 402.1 cm2
- A = ½ × π × r2 = ½ × π × 256
- ≈ 402.1 cm2
4.A circle has a circumference of 28π cm. Find its radius and its area (leave the area in terms of π).
Answer: r = 14 cm; A = 196π cm2
- C = 2πr, so 2πr = 28π
- r = 14 cm
- A = πr2 = 196π cm2
5.Find the area of a semicircle with a radius of 10 cm, correct to 1 decimal place.
Answer: 157.1 cm2
- A = ½ × π × r2 = ½ × π × 100
- ≈ 157.1 cm2
6.Find the area of a semicircle with a radius of 5 cm, correct to 1 decimal place.
Answer: 39.3 cm2
- A = ½ × π × r2 = ½ × π × 25
- ≈ 39.3 cm2
7.A circle has a radius of 16 cm. Find its area, correct to 1 decimal place.
Answer: 804.2 cm2
- A = π × r2 = π × 162 = π × 256
- ≈ 804.2 cm2
8.Find the area of a semicircle with a radius of 9 cm, correct to 1 decimal place.
Answer: 127.2 cm2
- A = ½ × π × r2 = ½ × π × 81
- ≈ 127.2 cm2
9.A circle has a circumference of 26π cm. Find its radius and its area (leave the area in terms of π).
Answer: r = 13 cm; A = 169π cm2
- C = 2πr, so 2πr = 26π
- r = 13 cm
- A = πr2 = 169π cm2
10.Find the area of a semicircle with a radius of 19 cm, correct to 1 decimal place.
Answer: 567.1 cm2
- A = ½ × π × r2 = ½ × π × 361
- ≈ 567.1 cm2
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.