qns from surface area and volumes?

Question

the internal and external diameters of a hollow hemispherical vessel are 24cm and 25cm recpectively . if the cost of painting 1 cm^ of the surface area is rs 5.25 find the total cost of painting the vessel all over.
take pie 22/7

pls explain the ans in detail
the ans is rs 10110.38

Answer 1

the internal area=2 pi 12^2
external area=2 pi 12.5^2
area of the annular ring=pi[(12.5)^2-(12)^]
total area to be painted
=288 pi+312.5 pi+12.25 pi
=612.75 pi cm^2
cost of painting=612.75*22/7*
= Rs.10110.38

Answer 2

Good job Raj. You remembered the annular ring.