PSLE The figure is made up of 6 identical quadrants and 3 identical semicircles. The radius of each quadrant is 21 cm. The unshaded area marked A is enclosed by 2 quadrants and 3 semicircles. (Take π = 3.14)
- Find the perimeter of N.
- Find the total shaded areas.
(a)
Diameter of the quadrant
= 2 x 21
= 42 cm
Perimeter of 2 quadrants
=
12 x 3.14 x 42
= 65.94 cm
Diameter of the semicircle
= 42 ÷ 3
= 14 cm
Perimeter of 3 semicircles
= 1
12 x 3.14 x 14
= 65.94 cm
Perimeter of N
= 65.94 + 65.94
= 131.88 cm
(b)
Area of the large circle
= 3.14 x 21 x 21
= 1384.74 cm
2
Radius of 1 semicircle
= 14 ÷ 2
= 7 cm
Area of 3 semicircles
= 1
12 x 3.14 x 7 x 7
= 230.79 cm
2 Area of 2 boomerangs
= Area of the rectangle - Area of the semicircle
= 42 x 21 -
12 x 3.14 x 21 x 21
= 882 - 692.37
= 189.63 cm
2 Total shaded areas
= 1384.74 - 230.79 - 189.63
= 964.32 cm
2 Answer(s): (a) 131.88 cm; (b) 964.32 cm
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