The figure shows a circle and 6 identical quarter circles. The radius of each quarter circle is 8 cm. Line XY passes through the centre of the circle. (Take π=3.14\pi = 3.14.)

  1. (a)

    Find the area of the shaded part.

  2. (b)

    Find the perimeter of the shaded part.

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Worked solution

16(a)

1. Find the radius of the large circle

The diameter of the large circle is made up of the bases of 3 quarter circles.
Diameter =3×8=24 cm= 3 \times 8 = 24\text{ cm}
Radius of large circle =24÷2=12 cm= 24 \div 2 = 12\text{ cm}

2. Calculate the area of the large circle

Area of large circle=π×122=144×3.14=452.16 cm2\text{Area of large circle} = \pi \times 12^2 = 144 \times 3.14 = 452.16\text{ cm}^2

3. Calculate the total area of the 6 quarter circles

Area of 6 quarter circles=6×14×π×82=1.5×64×3.14=96×3.14=301.44 cm2\text{Area of 6 quarter circles} = 6 \times \frac{1}{4} \times \pi \times 8^2 = 1.5 \times 64 \times 3.14 = 96 \times 3.14 = 301.44\text{ cm}^2

4. Find the area of the shaded part

Shaded area=Area of large circle−Area of 6 quarter circles\text{Shaded area} = \text{Area of large circle} - \text{Area of 6 quarter circles}
Shaded area=452.16−301.44=150.72 cm2\text{Shaded area} = 452.16 - 301.44 = 150.72\text{ cm}^2

Answer

150.72 cm2150.72\text{ cm}^2

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