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 + 15
Breadth of the rectangle
= 5 u
= 2 radii + 3
7 u - 5 u = (2 radii) + 15 - (2 radii + 3)
2 u = 15 - 3
2 u = 12
1 u = 12 ÷ 2 = 6
5 u = 5 x 6 = 30
Radius of the quarter circle
= (30 - 3) ÷ 2
= 27 ÷ 2
= 13.5 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 27
= 84.78 cm
Perimeter of the shaded part
= 84.78 + 15 + 15 + 3 + 3
= 120.78 cm
≈ 120.8 cm (Correct to 1 decimal place)
Answer(s): (a) 13.5 cm; (b) 120.8 cm