Math CentralQuandaries & Queries


Question from Craig:

I need to get dirt to fill an area 25ft x 25ft (think of a giant sandbox) HOWEVER, there is a pool 18 ft round in the middle of it. We need to backfill the area around the outside of the pool 6" deep. How much dirt will I need?

Hi Craig,

You can use our volume calculator to do this, but you need to use it twice. First find the volume of sand you would need to fill the entire sand box, 25 ft by 25 ft by 6 inches. Next find the volume of sand you don't need by calculating the volume of a cylinder that is "18 ft round" and 6 inches deep. The volume of sand you need is the difference between the results of these two calculations.


About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS