Question

a building tower resembles an inverted cone. the towers diameter is 20 ft, and its height is 21 ft. a contractor will fill the cone with concrete at $7.25 per cubic foot. what is the estimate of the total cost to fill this cone? use 3.14 for pi. $15,936 $6,936 $1,395 $19,963

Explanation:

Step1: Calculate the radius

The diameter $d = 20$ ft, so the radius $r=\frac{d}{2}=\frac{20}{2}=10$ ft.

Step2: Find the volume of the cone

The volume formula of a cone is $V=\frac{1}{3}\pi r^{2}h$. Substitute $r = 10$ ft, $h = 21$ ft and $\pi=3.14$ into the formula. So $V=\frac{1}{3}\times3.14\times10^{2}\times21=\frac{1}{3}\times3.14\times100\times21 = 2198$ cubic - feet.

Step3: Calculate the total cost

The cost per cubic - foot is $\$7.25$. Multiply the volume by the cost per cubic - foot: $C=7.25\times2198 = 15935.5\approx15936$.

Answer:

$\$15,936$