The volume of a cylinder is given by πr²h where, r is the radius of the cylinder and h is the height of the cylinder.
Also r=d/2 , where d is the diameter of the cylinder.
Therefore if the diameter is halved, the radius also gets halved ,i.e., it becomes r/2. Therefore the new volume = π(r/2)²h
=π(r²/4)h
=(1/4) πr²h
