1953 AHSME Problem 9

The number of ounces of water needed to reduce 9 ounces of shaving lotion containing 50 % alcohol to a lotion containing 30 % alcohol is:

\textbf{(A)}\ 3 \qquad \textbf{(B)}\ 4 \qquad \textbf{(C)}\ 5 \qquad \textbf{(D)}\ 6 \qquad \textbf{(E)}\ 7

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.