Question

The outer circumference of a circular race-track is 528 m . The track is everywhere 14 m wide. Calculate the cost of levelling the track at the rate of 50 paise per square metre.

`(use pi=22/7). `

Answer 1

Let the radius of the inner circle and the race track be R m.
Outer circumference of the race track = 528 m 

`⇒ 2 pi R=528` 

`⇒ R=528/2pi=84 m`

Total radius of the outer circle =` 84-14=70 m` 

Area of the circular track = Area of the outer circle − area of inner circle

`= pi(84)^2-pi(70)^2`

`= pi [(84-70)(84+70)]`

`=pi(14)(154)` 

`=6776 m^2`

Cost of levelling the track =` 0.5xx6776=Rs 3388`