PSLE The figure shows a rectangle with its corners cut out. Each of the 4 identical corners cut out is a quarter circle. The ratio of the length of the rectangle to its breadth is 7 : 5.
- What is the radius of each quarter circle?
- What is the perimeter of the shaded part. Take π = 3.14. Give your answer correct to 1 decimal place.
Length of the rectangle
= 7 u
= 2 radii + 19
Breadth of the rectangle
= 5 u
= 2 radii + 3
7 u - 5 u = (2 radii) + 19 - (2 radii + 3)
2 u = 19 - 3
2 u = 16
1 u = 16 ÷ 2 = 8
5 u = 5 x 8 = 40
Radius of the quarter circle
= (40 - 3) ÷ 2
= 37 ÷ 2
= 18.5 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 37
= 116.18 cm
Perimeter of the shaded part
= 116.18 + 19 + 19 + 3 + 3
= 160.18 cm
≈ 160.2 cm (Correct to 1 decimal place)
Answer(s): (a) 18.5 cm; (b) 160.2 cm