Question

The inner circumference of a circle track is $330m$. The track is $10.5m$ wide everywhere . Calculate the cost of putting up a fence along the outer circle at the rate of $Rs.20$ per meter.

Answer 1

Let $r$ and $R$ be the inner and outer radii of circular track respectively.

Inner circumference $=330m$

$\Rightarrow 2\pi r=330$

$\Rightarrow r=\frac{330}{2\times \frac{22}{7}}$

$\Rightarrow r=\frac{330\times 7}{44}=52.5m$

Therefore,

Outer radius $=r+10.5=52.5+10.5=63m$

Outer circumference $=2\pi R=2\times \frac{22}{7}\times 63=396m$

Cost of putting fencing on $1m=Rs.20$

Tjherefore,

Cost of putting fencing on $396m=20\times 396=Rs.7920$