A cylindrical tube, open at both ends, is made of metal. The internal diameter of the tube is 10.4 cm and its length is 25 cm. The thickness of the metal is 8 mm everywhere. Calculate the volume of the metal.
Given,
Internal diameter of tube = 10.4 cm
Internal radius of tube = 
Thickness of metal = 8 mm = 0.8 cm
External radius of tube = 5.2 + 0.8 = 6 cm
Length of tube = 25 cm
∴ Volume of metal = (external volume – internal volume)
= πh (62 – 5.22) = 
16