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 + 24
Breadth of the rectangle
= 3 u
= 2 radii + 4
5 u - 3 u = (2 radii) + 24 - (2 radii + 4)
2 u = 24 - 4
2 u = 20
1 u = 20 ÷ 2 = 10
3 u = 3 x 10 = 30
Radius of the quarter circle
= (30 - 4) ÷ 2
= 26 ÷ 2
= 13 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 26
= 81.64 cm
Perimeter of the shaded part
= 81.64 + 24 + 24 + 4 + 4
= 137.64 cm
≈ 137.6 cm (Correct to 1 decimal place)
Answer(s): (a) 13 cm; (b) 137.6 cm