An hour-glass is formed by two identical cones.

Initially, the top cone is full of sand, and the bottom cone is empty.

The sand starts flowing down at a constant rate and the top cone is emptied in exactly 1:30 hours.

How long does it take for the height of the sand in the bottom cone be half of the height in the top cone?

(In reply to Sand vs. Water? by rod hines)

yes, the 8/27 is (2/3)^3, based on the fact the two 3-d shapes are similar with linear dimensions on the 2/3 ratio.

Posted by Charlie on 2009-01-21 11:24:18