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 + 28
Breadth of the rectangle
= 7 u
= 2 radii + 7
10 u - 7 u = (2 radii) + 28 - (2 radii + 7)
3 u = 28 - 7
3 u = 21
1 u = 21 ÷ 3 = 7
7 u = 7 x 7 = 49
Radius of the quarter circle
= (49 - 7) ÷ 2
= 42 ÷ 2
= 21 cm
(b)
Perimeter of the 4 quarter circles
= 3.14 x 42
= 131.88 cm
Perimeter of the shaded part
= 131.88 + 28 + 28 + 7 + 7
= 201.88 cm
≈ 201.9 cm (Correct to 1 decimal place)
Answer(s): (a) 21 cm; (b) 201.9 cm