PSLE The figure is made up of 6 identical quadrants and 3 identical semicircles. The radius of each quadrant is 18 cm. The unshaded area marked A is enclosed by 2 quadrants and 3 semicircles. (Take π = 3.14)
- Find the perimeter of V.
- Find the total shaded areas.
(a)
Diameter of the quadrant
= 2 x 18
= 36 cm
Perimeter of 2 quadrants
=
12 x 3.14 x 36
= 56.52 cm
Diameter of the semicircle
= 36 ÷ 3
= 12 cm
Perimeter of 3 semicircles
= 1
12 x 3.14 x 12
= 56.52 cm
Perimeter of V
= 56.52 + 56.52
= 113.04 cm
(b)
Area of the large circle
= 3.14 x 18 x 18
= 1017.36 cm
2
Radius of 1 semicircle
= 12 ÷ 2
= 6 cm
Area of 3 semicircles
= 1
12 x 3.14 x 6 x 6
= 169.56 cm
2 Area of 2 boomerangs
= Area of the rectangle - Area of the semicircle
= 36 x 18 -
12 x 3.14 x 18 x 18
= 648 - 508.68
= 139.32 cm
2 Total shaded areas
= 1017.36 - 169.56 - 139.32
= 708.48 cm
2 Answer(s): (a) 113.04 cm; (b) 708.48 cm
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