Question 1188054
the well is 40 feet deep.
the diameter of the well is 6.5 feet in diameter.
it is lined with 1.5 feet thick wall of stone so that the inner diameter of the well becomes 3.5 feet.


the volume of the cylinder is equal to pi * r^2 * h.


the outer volume of the well, including the stone walls, is equal to pi * (6.5/2)^2 * 40 * pi = 422.5 * pi cubic feet.


the inner volume of the well is equal to (3.5)^2 * 40 * pi = 122.5 * pi cubic feet.


the difference between the inner volume and the outer volume is equal to 422.5 * pi minus 122.5 * pi = 300 cubic feet.


that's the number of cubic feet of stone in the well.


pi is equal to a constant value of 3.141592654.


422.5 * pi cubic feet = 1327.322896 cubic feet.
122.5 * pi cubic feet = 384.8451001 cubic feet.


the number of cubic feet of stone is equal to 300 * pi cubic feet = 942.4777961 cubic feet.


let me know if you have any questions.


theo