Puzzle Answer

Answer: You must turn over the 8 and the brown card.

Explanation: The proposition can be written as

Even → Red

but be careful, this is not an if and only if proposition!

So obviously you need to turn over the 8.  If that card is not red on the other side then the proposition is false. You also need to turn over the brown card.  If the brown card is even then the proposition is false.  You do not need to worry about the 3.

The card that tricks most people is the red card.  Since we’re asked to establish if the proposition is false, turning over the red card won’t tell us anything. If it’s even the proposition is true, but if the other side is odd the proposition says nothing about odd cards not being red.