A hollow sphere of internal and external diameters 4 cm and 8 cm respectively is melted into a cone of base diameter 8 cm. Calculate the height of the cone.
Given, internal radius of hollow sphere, r = (4/2) = 2cm
External radius = 8/2 = 4cm
Volume of hollow sphere = 
--------(i)
Given, diameter of the cone = 8cm
∴ Radius of the cone = 4 cm
Let height of the cone be h
Volume of the cone = 
--------(ii)
Since hollow sphere is melted into a cone so their volumes are equal,
∴ h = 12cm
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