A hollow cylindrical pipe is 56 cm long. Its outer and inner radii are 20 cm and 16 cm respectively. Find the volume of the iron used in making the pipe.
Concept Used: Volume of the iron used = External volume – Internal volume
Volume of Cylinder = πr2h
Where r = radius of the cylinder and h = height of the cylinder.
Given: Outer Radii = 20 cm
Inner radii = 16 cm
Height of pipe = 56 cm
Assumption: Let r1 be the radius of the inner cylindrical portion and r2 be the radius of the outer cylindrical portion. And h be the height of Cylinder.
Explanation:
Volume of iron Used = πr12h2 – πr22h2
Volume of Iron Used = πh(r12 – r22 )
The volume of Iron Used 
The volume of Iron Used = [22 × 8 × (400 – 256)] cm3
The volume of Iron Used = [22 × 8 × 44] cm3
The volume of Iron Used = 7744 cm3
Hence, The volume of the Iron Used is 7744 cm3.