1985 AJHSME Problem 25

Five cards are lying on a table as shown.

\begin{matrix} & \qquad & \underline{\,\tt{P}\,} & \qquad & \underline{\,\tt{Q}\,} \\ \\ \underline{\,\tt{3}\,} & \qquad & \underline{\,\tt{4}\,} & \qquad & \underline{\,\tt{6}\,} \end{matrix}

Each card has a letter on one side and a whole number on the other side. Jane said, "If a vowel is on one side of any card, then an even number is on the other side." Mary showed Jane was wrong by turning over one card. Which card did Mary turn over?

\textbf{(A)}\ 3 \qquad \textbf{(B)}\ 4 \qquad \textbf{(C)}\ 6 \qquad \textbf{(D)}\ \text{P} \qquad \textbf{(E)}\ \text{Q}

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