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 8 : 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
= 8 u
= 2 radii + 21
Breadth of the rectangle
= 5 u
= 2 radii + 6
8 u - 5 u = (2 radii) + 21 - (2 radii + 6)
3 u = 21 - 6
3 u = 15
1 u = 15 ÷ 3 = 5
5 u = 5 x 5 = 25
Radius of the quarter circle
= (25 - 6) ÷ 2
= 19 ÷ 2
= 9.5 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 19
= 59.66 cm
Perimeter of the shaded part
= 59.66 + 21 + 21 + 6 + 6
= 113.66 cm
≈ 113.7 cm (Correct to 1 decimal place)
Answer(s): (a) 9.5 cm; (b) 113.7 cm