A right circular cone of diameter r cm and height 12cm rests on the base of a right circular cylinder of radius r cm. Their bases are in the same plane and the cylinder is filled with water to a height of 12cm.if the cone is removed, then find height to which the water level will fall.



If the cone is removed, the water level will change according to how the cylinder and cone were placed. 
If it was like this, 
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Then all the water would fall off as the height of the cone and the water level are same. 
If it is the upside down position of the above figure, then the water would fall according to the height of the cylinder
cone is fully filled with water. the amount of water will be equal to the v of the the cone. 
v of the cone= 1/3 pi*r*r*h 
v of the cilinder=pi*r*r*h 
1/3*pi*r*r*12=pi*r*r*h =12/3=4 
water will rise by 4cms