AHSME 1973 Problem 33

When one ounce of water is added to a mixture of acid and water, the new mixture is $20\%$ acid. When one ounce of acid is added to the new mixture, the result is $33\frac13\%$ acid. The percentage of acid in the original mixture is $\textbf{(A)}\ 22\% \textbf{(B)}\ 24\% \textbf{(C)}\ 25\% \textbf{(D)}\ 30\% \textbf{(E)}\ 33\frac13 \%$