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 10 : 7.
- 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
= 10 u
= 2 radii + 17
Breadth of the rectangle
= 7 u
= 2 radii + 5
10 u - 7 u = (2 radii) + 17 - (2 radii + 5)
3 u = 17 - 5
3 u = 12
1 u = 12 ÷ 3 = 4
7 u = 7 x 4 = 28
Radius of the quarter circle
= (28 - 5) ÷ 2
= 23 ÷ 2
= 11.5 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 23
= 72.22 cm
Perimeter of the shaded part
= 72.22 + 17 + 17 + 5 + 5
= 116.22 cm
≈ 116.2 cm (Correct to 1 decimal place)
Answer(s): (a) 11.5 cm; (b) 116.2 cm