Three hundred books sell for $40$ dollars each. For each $5$ dollar increase in the price, $25$ fewer books are sold. Write the revenue $R$ as a function of the number $x$.
For two situations: $x=$ number of books and another equation for $x=$ five dollar increases.
Well the equation that I got for $x$ being $5$ dollar increases is $R(x)=(40+5x)(300-25x)$. I am not quite sure what the $x$ means in this question. That is why I am trying to get an equation for both possibilities maybe?
On
You have the correct formula for $x$ being the number of \$5 increases. It does not really make sense to use $x$ as the number of books sold as you need to know both the price and the number of books to find revenue. But if you want to use it, just calculate number of price increases as $n=\frac{300-x}{25}$ and put it in your original formula.
You are right, the question is not clear.
When $x$ is the number of $5$-dollar change: $$R=(40+5x)(300-25x).$$ When $x$ is the number of books sold: $$R=\frac{500-x}{5}\cdot x.$$