The radius of a sphere shrinks from 10 cm to 9.8 cm. Find approximately the decrease in (i) volume, and (ii) surface area.
Decrease in radius = dr = 10-9.8
∴ dr = 0.2
Volume of the sphere is given by = 
Change in volume = 
∴ 
⇒ 
Surface area of the sphere is given by = 
Change in volume = 
∴ dA = 8π×10× 0.2
∴ dA = 16π.
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