Maths-
General
Easy
Question
The diameter of a circular park is 104 m. A road of width 3.5 m is on the outside around it. Find the cost of constructing the road at Rs. 15 per square meter.
Hint:
Try to find area of the road
The correct answer is: Rs. 17737.5
Since the road of width 3.5 m is on outside , it means
Diameter of inner circle = 104 m
Radius = 
= 
= 52 m
Radius of outer circle = Radius of inner circle + Width of road
= 52 + 3.5 = 55.5 m
We know that area of a circle = 
r2
Area of the road = Area of outer circle – Area of inner circle
= 
× (55.5)2 - × 52
= × ( 55.5 – 52)(55.5 + 52)
(
a2 – b2) = (a – b)(a + b)
= 3.5 × 107.5
= 1182.5 m2
Now, Cost of constructing 1 m2 road = Rs. 15
Cost of constructing 1182.5 m2 road = Rs. 15 × 1182.5
= Rs. 17737.5
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