2011 Pascal Problem 6

Peyton puts 30 L of oil and 15 L of vinegar into a large empty can. He then adds 15 L of oil to create a new mixture. What percentage of the new mixture is oil?

\textbf{(A)}\ 75\quad \textbf{(B)}\ 25\quad \textbf{(C)}\ 45\quad \textbf{(D)}\ 50\quad \textbf{(E)}\ 60

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Pascal contests here.