College Algebra, Chapter 1, 1.2, Section 1.2, Problem 50

Suppose that a health clinic uses a solution of bleach. A tank contains $100$ gal of a solution of $2\%$ ordinary bleach mixed with pure distilled water. For complete sterilization, a new research indicates that the concentration of the bleach should be $5\%$. How much of the solution should be drained and replaced with bleach to increase the bleach content to the recommended level?










$
\begin{equation}
\begin{aligned}

100(0.02) - x(0.02) + x(1) =& (100 - x + x)(0.05)
&& \text{Model, simplify}
\\
\\
2 - 0.02x + x =& 5
&&
\\
\\
0.98x =& 3
&& \text{Solve for } x
\\\\
x =& \frac{3}{0.98} \text{ gal}
&&

\end{aligned}
\end{equation}
$