Question

A water storage tank has the shape of a cylinder with diameter 14 ft. It is mounted so that the circular cross-sections are vertical. If the depth of the water is 11 ft, what percentage of the total capacity is being used? (Round your answer to one decimal place.)

Answer 1

Check the picture below.

neverminding for a few seconds the volume of the cylinder, the percentage in the height used by the water will be the same as the percentage of its volume.  We know the total amount or 100% of the height is 14, so what is 11 in percentage?

$\begin{array}{ccll} amount&\%\\ \cline{1-2} 14&100\\ 11&x \end{array}\implies \cfrac{14}{11}=\cfrac{100}{x}\implies 14x=1100 \\\\\\ x = \cfrac{1100}{14}\implies x = \cfrac{550}{7}\implies \boxed{x \approx 78.6}$