Question

The internal and external diameters of a hollow hemi-spherical vessel are 24 cm and 25 cm respectively. The cost of painting 1 square cm of the surface is Rs 1.7. Find the total cost to paint the vessel all over (ignore the area of edge).

The nearest integer to the answer is

Answer 1

Given, internal and external diameters of a hollow hemi-spherical vessel are 24 cm and 25 cm respectively.
Therefore, internal radius (r) = 12 cm and external radius (R) $=12.5cm$
Total area to be painted $=2\pi R^2-2\pi r^2=2\pi ({12.5}^2-{12}^2)$
$=2\times \frac{22}{7}\times \left(12.25\right)=77c{m}^2$
Given, cost of painting 1 square cm of the surface is $Rs1.7$.
Therefore, total cost of painting $77c{m}^2$ surface area $=Rs1.7\times 77=Rs131.1=131$