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 5 : 3.
- 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
= 5 u
= 2 radii + 26
Breadth of the rectangle
= 3 u
= 2 radii + 6
5 u - 3 u = (2 radii) + 26 - (2 radii + 6)
2 u = 26 - 6
2 u = 20
1 u = 20 ÷ 2 = 10
3 u = 3 x 10 = 30
Radius of the quarter circle
= (30 - 6) ÷ 2
= 24 ÷ 2
= 12 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 24
= 75.36 cm
Perimeter of the shaded part
= 75.36 + 26 + 26 + 6 + 6
= 139.36 cm
≈ 139.4 cm (Correct to 1 decimal place)
Answer(s): (a) 12 cm; (b) 139.4 cm