PSLE The figure shows 6 circles, each of radius 21 cm. Each circle touches the circles next to it.
(Take π =
227)
- Find the perimeter of the shaded part.
- Find the area of the shaded part.
(a)
Diameter of each circle
= 2 x 21
= 42 cm
Perimeter of the shaded part
= Circumference of 3 circles
= 3 x
227 x 42
= 396 cm
(b)
Length of the dotted rectangle
= 4 x 21
= 84 cm
Breadth of the dotted rectangle
= 2 x 21
= 42 cm
Area of the dotted rectangle
= 84 x 42
= 3528 cm
2 Area of 2 semicircles
= Area of 1 circle
=
227 x 21 x 21
= 1386 cm
2 Area of the shaded part
= 3528 + 1386
= 4914 cm
2 Answer(s): (a) 396 cm; (b) 4914 cm
2