Give your answer to 1 decimal place
Area and circumference — Notes & Worked Examples Show / Hide
Explanation:
For any circle with radius r and diameter d = 2r: the Circumference (perimeter) is C = πd (or 2πr), and the Area is A = πr². Always check whether the question gives you the radius or the diameter before starting!
If the question asks for your answer in terms of π (non-calculator), leave π as a symbol in your answer (e.g. 25π cm²). Remember that the perimeter of a semicircle includes the straight diameter as well as the curved arc: Perimeter = 12πd + d.
Example 1: A circle has a diameter of 12 cm. Work out its area and circumference to 1 d.p.
Example 2: Work out the perimeter of a semicircle with radius 5 cm. Give your answer to 1 d.p.
Give your answer to 1 decimal place
Give your answer to 1 decimal place
Worked Solution & Answer
Worked Solution & Answer
AC is the diameter of semicircle X and B is the centre of semicircle X
BD is the diameter of semicircle Y and C is the centre of semicircle Y
CE is the diameter of semicircle Z and D is the centre of semicircle Z
AC = BD = CE = 20 cm
Work out the perimeter of the shaded shape.
Give your answer correct to the nearest whole number.
Worked Solution & Answer
Straight segments AB = 10 cm and DE = 10 cm M1
Perimeter = 3 × 10π + 10 + 10 = 30π + 20 = 114.247... ≈ 114 cm. A1
The inner semicircle has a radius of 7 metres.
The path has a width of 2 metres.
Work out the perimeter of the path.
Give your answer correct to one decimal place.
Worked Solution & Answer
Outer radius = 7 + 2 = 9 m, outer arc = π × 9 = 9π ≈ 28.274 m M1
Total perimeter = 7π + 9π + 2 + 2 = 16π + 4 = 54.265... ≈ 54.3 m. A1
Worked Solution & Answer
The diameter of the semicircle is 8 cm
Worked Solution & Answer
Area of circle = π × 102 = 100π M1
Radius of semicircle = 8 ÷ 2 = 4 cm M1
Area of shaded semicircle = 12 × π × 42 = 8π M1
Unshaded area = 100π - 8π = 92π
Ratio = 92π8π = 928 = 11.5 A1
Worked Solution & Answer
Total perimeter = 78.5398 + 50 = 128.5398 m M1
Fence cost = 128.5398 × 29.86 = £3838.20 M1
Total cost = 3838.20 + 3 × 180 = £4378.20 A1
250 millilitres of wood varnish covers 4 m2 of the wood.
Work out how many millilitres of wood varnish Julie will need.
Give your answer correct to the nearest millilitre.
Worked Solution & Answer
Area of semicircle = ½ × π × 0.25² = 0.09817... m² M1
Wood area = 1.5 – 0.09817... = 1.4018... m² M1
Two coats = 2.80365... m² M1
Varnish needed = (2.80365... ÷ 4) × 250 = 175.228... = 175 ml A1
He is going to cover the garden with grass seed to make a lawn.
Grass seed is sold in boxes.
Each box of grass seed will cover 46 m2 of garden.
You must show your working. [4 marks]
Give a reason for your answer. [1 mark]
Worked Solution & Answer
Boxes ≈ 300 ÷ 50 = 6 (or 314 ÷ 45 ≈ 7) A1