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Year 9 Circumference and Area of Circles Worksheet — Level 3 — Answers

Answer sheet with worked solutions for the Year 9 area & perimeter worksheet.

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Success TutoringWorksheetsAnswer sheetYear 9 · Mathematics · Area & Perimeter

Year 9 Circumference and Area of Circles Worksheet — Level 3 — Answers

Show your working. 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

  1. C = 2πr, so 2πr = 40π
  2. r = 20 cm
  3. A = πr2 = 400π cm2
2.A circle has a circumference of 6π cm. Find its radius and its area (leave the area in terms of π).

Answer: r = 3 cm; A = 9π cm2

  1. C = 2πr, so 2πr = 6π
  2. r = 3 cm
  3. A = πr2 = 9π cm2
3.A circle has a circumference of 18π cm. Find its radius and its area (leave the area in terms of π).

Answer: r = 9 cm; A = 81π cm2

  1. C = 2πr, so 2πr = 18π
  2. r = 9 cm
  3. A = πr2 = 81π cm2
4.A circle has a circumference of 10π cm. Find its radius and its area (leave the area in terms of π).

Answer: r = 5 cm; A = 25π cm2

  1. C = 2πr, so 2πr = 10π
  2. r = 5 cm
  3. A = πr2 = 25π cm2
5.Find the area of a semicircle with a radius of 7 cm, correct to 1 decimal place.

Answer: 77.0 cm2

  1. A = ½ × π × r2 = ½ × π × 49
  2. ≈ 77.0 cm2
6.A circle has a radius of 16 cm. Find its area, correct to 1 decimal place.

Answer: 804.2 cm2

  1. A = π × r2 = π × 162 = π × 256
  2. ≈ 804.2 cm2
7.A circle has a diameter of 38 cm. Find its area, correct to 1 decimal place.

Answer: 1134.1 cm2

  1. r = 38 ÷ 2 = 19 cm
  2. A = π × r2 = π × 192 = π × 361
  3. ≈ 1134.1 cm2
8.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

  1. C = 2πr, so 2πr = 28π
  2. r = 14 cm
  3. A = πr2 = 196π cm2
9.A circle has a circumference of 8π cm. Find its radius and its area (leave the area in terms of π).

Answer: r = 4 cm; A = 16π cm2

  1. C = 2πr, so 2πr = 8π
  2. r = 4 cm
  3. A = πr2 = 16π cm2
10.Find the area of a semicircle with a radius of 5 cm, correct to 1 decimal place.

Answer: 39.3 cm2

  1. A = ½ × π × r2 = ½ × π × 25
  2. ≈ 39.3 cm2
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