Math CentralQuandaries & Queries


Question from Gene:

How many yards of concrete to put a 28' round is to be 4 inches deep


Are you looking for a slab for the bottom of the pool that has a diameter of 28 feet and 4 inches thick?






Since you want the volume in cubic yards (sometimes just called yards) you should change the dimensions to yards. There are 3 feet in a yard and hence 28 feet is 28/3 yards. There are 36 inches in a yard and hence 4 inches is 4/36 yards.

The volume of a cylindrical slab is π r2 h where r is the radius and h is the height or thickness. The radius is half the diameter (14/3 yards) and thus you slab has a volume of

π r2 h = π (14/3)2 × 4/36 = 7.6 yards.


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