Question

As a water quality assurance employee for your local Aqua America, Inc., branch, you record a drop in water levels from 28 feet to 7 feet at your reservoir. What is the percentage decrease?

Answer 1

so, it went down from 28 to 7, meaning 28 - 7 = 21, 21 feet then.

now, if we take 28 to be the 100%, what is 21 off of it in percentage?


`\bf \begin{array}{ccll} amount&\%\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ 28&100\\ 21&p \end{array}\implies \cfrac{28}{21}=\cfrac{100}{p}\implies p=\cfrac{21\cdot 100}{28}`