A cylindrical tube opened at both the ends is made of iron sheet which is 2 cm thick. If the outer diameter is 16 cm and its length is 100 cm, find how many cubic centimetres of iron has been used in making the tube?
Given: Outer diameter d = 16cm
Thus, 
Height = length = 100cm
Thickness of iron sheet = 2cm
To find: Volume of iron used
Volume of cylinder = πr2h
Where r= outer radius
And π = 3.14
Thus, Volume of cylinder = πr2h = 3.14 × (8)2× 100
= 20,096 cm3
Now, inner diameter = outer diameter – 2× thickness of iron sheet
inner diameter = 16-(2× 2) = 12cm
Thus, Volume of hollow space = πR2 h
Where R= inner radius
And π = 3.14
Thus, Volume of hollow space = πR2 h = 3.14 × (6)2× 100
= 11,304 cm3
Thus,
Volume of iron used = Volume of cylinder – Volume of hollow space
= (20,096 – 11,304 ) cm3
= 8800 cm3