There are $2$ boys for every $3$ girls in Ms. Johnson's math class.  If there are $30$ students in her class, what [percent](https://artofproblemsolving.com/wiki/index.php/Percent) of them are boys?
$\text{(A)}\ 12\% \qquad \text{(B)}\ 20\% \qquad \text{(C)}\ 40\% \qquad \text{(D)}\ 60\% \qquad \text{(E)}\ 66\frac{2}{3}\%$
Besides ensuring the situation is possible, the $30$ students information is irrelevant.
From the first statement, we can deduce that $2$ of every $2+3=5$ students are boys.  Thus, $2/5=40\% \rightarrow \boxed{\text{C}}$ of the students are boys.