Math CentralQuandaries & Queries


Question from Brett, a student:

I am studying for my builders license and I am having trouble figuring out
cubic yards of concrete in a footing.

My question that I am having trouble with is.

You need to pour an 8"x16" footing that is 100ft. long. At a cost of
$65 per cubic yard, how much will this cost?

(A) $205 or less
(B) more than $205, but less than $220
(C) $220 to $235(D) more than $235

The answer they give is (B)

I keep coming up with $240.75

Hi Brett,

I would convert all the dimensions to yards first so that the resulting volume calculation is in cubic yards.

8" = 8/36 yards
16" = 16/36 yards
100 feet = 100/3 yards.

Thus the volume is

(8/36) × (16/36) × (100/3) = 3.29 cubic yards.

At $65 per cubic yards that's

3.29 × $65 = $213.99

I hope this helps,

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