A road 3.5 m wide surrounds a circular park whose circumference is 88 m. Find the cost of paving the road at the rate of ₹60 per square metre.

Given,

Circumference of circular park = 88 m

Let radius of circular park be r meters.

2πr = 88

$\Rightarrow 2 \times \dfrac{22}{7} \times r = 88 \\[1em] \Rightarrow r = \dfrac{88 \times 7}{2 \times 22} \\[1em] \Rightarrow r = 14 \text{ m}.$

From figure,

Radius of outer circle (R) = Radius of circular park + Width of road = 14 + 3.5 = 17.5 m

Area of road = Area of outer circle - Area of circular park

= πR² - πr²

= π(17.5)² - π(14)²

= π[306.25 - 196]

= 110.25π

= $110.25 \times \dfrac{22}{7}$ = 346.5 m².

Cost of paving the road = Area of road × Rate = 346.5 × 60 = ₹ 20790.

Hence, cost of paving road = ₹ 20790.