



 
Malik, I find this problem strange. I don't think the rates given are necessary to solve it. The physical fact that is the key to the solution is that slope of the right circular cone of sand is a constant, that is if r is the radius of the pile in centimeters at time t minutes and h is the height in centimeters at the same time then r/h is a constant, regardless of the time. The volume of a right circular cone is 1/3 π r^{2} h. You are told that the volume is 600 cm^{3} when r = 12 cm at some specific time and hence at this time
Solve for h and then find r/h at this time. When the pile touches the bottom of the container h = 30 cm. At this time r/h has the same value as you found in the previous step. Solve for r. Now you know r and h when the pile touches the container so you can calculate the volume of the pile. I hope this helps,  


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