The internal and external diameters of a hollow hemispherical vessel are 21 cm and 25.2 cm respectively. The cost of painting 1 cm2 of the surface is 10 paise. Find the total cost to paint the vessel all over.
Given that, internal diameter of hollow hemisphere, r = 10.5cm
External radius, R = 12.6cm
Total surface area = 2πR2 +2πr2 + π(R2 - r2)
=2π(12.6)2 +2π(10.5)2 + π((12.6)2 – (10.5)2)
=1843.38 cm2
Given that, cost of painting 1 cm2 of surface = 10paise
Therefore, total cost to paint 1843.38 cm2 = 
24