The internal and external diameters of a hollow hemispherical vessel are 24cm and 25cm respectively. The cost to paint `1c m^2` the surface is Rs. 0.05. Find the total cost to paint the vessel all over. `(u s epi=(22)/7)`

Explanation

Given : Internal diameter, `d=24cm` and Outer diameter,`D=25cm`

So, Internal radius, `r=12cm` and `R=12.5cm`

`therefore` S.A of hemispherical vessel = `2pi(R^2+r^2)` = `2pi(12.5^2+12^2)` = `1887.28 cm^2`

Surface area of ring = `pi(R^2-r^2)` = `22/7(12.5^2-12^2)` = `943.64 cm^2`

Total area = `1887.28 + 943.64` = `2830.92 cm^2`

Hence, Cost of paint = `2830.92 xx 0.05` = Rs. `141.546`