Math CentralQuandaries & Queries


Question from arlene, a parent:

What is the total cost of a driveway that is 25' wide and 45' long with 4" thickness if the concreat cost 92.00 per cubic yard and labor is 70.00 a cubic yard?

Hi Arlene.

Cubic yards are a volume measurement, so you need to convert the driveway into a volume measurement as well in order to proceed to the cost.

Treat the driveway like a big flat box. First convert the the length measurements to compatible units. Since two measurements are in feet, I can convert the thickness from inches to feet by dividing it by twelve, then I can multiply length times width times depth and get a volume measurement.


You see that because I multiplied feet times feet times feet, my result is in feet^3 (cubic feet). But my cost rates are based on cubic yards, so I have to convert. To convert feet to yards, I divide by 3. Therefore to convert from feet^3 to yards^3, I divide by 3^3, and 3^3 = 27. So I divide by 27:


Finally, I have to multiply by the cost per cubic yard to get the total bill.


Stephen La Rocque

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