Question

The slant height of the frustum of a cone is $4cm$. If the perimeters of its circular bases be $18cm$ and $6cm$, find the curved surface area of the frustum and also find the cost of painting its total surface at the rate of Rs. $12.50$ per $100{cm}^2$

Answer 1

R.E.F image

$2\pi R=18$ $2\pi r=4$

$\pi R=9$ $\pi r=2$

$R=\frac{9}{\pi }$ $r=\frac{2}{\pi }$

Curved surface area $=\pi (R+2)l$

$=(\frac{9}{\pi }+\frac{2}{\pi })4$

$=44c{m}^2$

Total cost $=\frac{12.50}{100}\times 44$

$=5.5Rs$