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 + 19
Breadth of the rectangle
= 7 u
= 2 radii + 4
10 u - 7 u = (2 radii) + 19 - (2 radii + 4)
3 u = 19 - 4
3 u = 15
1 u = 15 ÷ 3 = 5
7 u = 7 x 5 = 35
Radius of the quarter circle
= (35 - 4) ÷ 2
= 31 ÷ 2
= 15.5 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 31
= 97.34 cm
Perimeter of the shaded part
= 97.34 + 19 + 19 + 4 + 4
= 143.34 cm
≈ 143.3 cm (Correct to 1 decimal place)
Answer(s): (a) 15.5 cm; (b) 143.3 cm