Question

The internal and external diameters of a hollow spherical vessel are $21cm$ and $25.2cm$ respectively. The cost of painting $1{cm}^2$ of the surface is $1.50$ paise. Find the total cost to paint the vessel all over.

Answer 1

Area $=4\pi R^2-4\pi r^2$

$=4\pi [{\left(\frac{25.2}{2}\right)}^2-{\left(\frac{21}{2}\right)}^2]$

$=4\times \frac{22}{7}\times \frac{4851}{100}$

$=\frac{15246}{25}$

$=609.84c{m}^2$

$\Rightarrow Cost=1.5\times 609.84$

$=914.76Rs$

Hence, the answer is $\mathrm{914.76.}$.