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$\newcommand{\pinover}[2]{\overset{\overset{\displaystyle\mathrm{\ #2\ }}{|}}{\strut #1 \strut}}\newcommand{\amp}{&}$

Last month, a full tank of gas for a car you drive cost you $\$40.00\text{.}$ You hear on the news that gas prices have risen by $12\%\text{.}$ By how much, in dollars, has the cost of a full tank gone up?

A full tank of gas now costs

more than it did last month.

Solution

Let $x$ represent the amount of increase. We can set up and solve the equation:

$\begin{aligned} \pinover{0.12}{12\%}\pinover{\cdot}{of}\pinover{40}{old\ cost}\amp\pinover{=}{is}\pinover{x}{how\ much}\\ 4.8\amp=x \end{aligned}$

A full tank now costs $\$4.80$ more than it did last month.