Quandaries and Queries


  I need to find out how much sand I would need to order for the base of a horse round pen.  The pen is 40 ft across and I would like a depth of 4 inches.  I have to order the sand in cubic yards.  I am a female senior citizen and I don't have a clue how to figure it.  Please help!  Thanks so much....


Hi Renee,

You have a circular slab of sand with a radius of 20 feet and a thickness of 4 inches.

The volume of a circular slab is

r2 t

where r is the radius and t is the thickness.

Since you want the volume in cubic yards I would first convert all the measurements to yards. There are 3 feet in a yard so 20 feet is 20/3 yards. 4 inches is one-third of a foot so 4 inches is

 1/3 3 = 1/9 yards.

Thus the volume is

(20/3)2 1/9 = 15.5 cubic yards.



Go to Math Central