Question

The price of an American Airlines ticket to Boston increased to $600. This is a 15 percent increase. What was the old fare? Round to the nearest cent.

Answer 1

The old fare was "x"
then it got bumped up by 15%, and the new price is x + 15% of x,
so.. one could say, that "x" is the 100%, then you add a 15% to
it, to get 600
thus $\bf \begin{array}{ccllll} amount&\%\\ \textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\ x&100\\ 600&100+15 \end{array}\implies \cfrac{x}{600}=\cfrac{100}{100+15}$

solve for "x"