Adams plans a profit of $10$ % on the selling price of an article and his expenses are $15$ % of sales. The rate of markup on an article that sells for $ $5.00$ is: 
$\textbf{(A)}\ 20\% \qquad \textbf{(B)}\ 25\% \qquad \textbf{(C)}\ 30\% \qquad \textbf{(D)}\ 33\frac {1}{3}\% \qquad \textbf{(E)}\ 35\%$
Let the cost of the product be C, and the selling price be S. Since Adams wants a 10% profit on the sale, and his expenses are 15% of the sale, we add $0.10S$ and $0.15S$ to the cost to get the selling price.
Then, $S=C+0.15S+0.10S \Rightarrow 0.75S=C \Rightarrow S=\frac{4}{3}C \Rightarrow \fbox{D}$.