Question

An hourglass consists of two sets of congruent composite figures on either end. Each composite figure is made up of a cone and a cylinder.
Each cone of the hourglass has a height of 15 millimeters. The total height of the sand within the top portion of the hourglass is 45 millimeters. The radius of both cylinder and cone is 6 millimeters. Sand drips from the top of the hourglass to the bottom at a rate of 10π cubic millimeters per second. How many seconds will it take until all of the sand has dripped to the bottom of the hourglass?
Answer

29

18

126

108

Answer 1

Find the volume of the sand, and then divide the volume by the rate to come up with the time.

Disclaimer: When we're doing the calculation for the volume of the cone below, it's really only an estimate. We're assuming it's really a cone (i.e. that it comes to a point); but if that were the case, no sand would be able to fall. Nevertheless, that's how we're doing it.

The total volume of sand consists of the sand in the cone portion plus whatever sand is in the cylindrical portion of the hourglass. We'll call the total volume V, the conical volume Vcn, and the cylindrical volume Vcy.

V = Vcn + Vcy

Answer 2

gotcha thanks!