If a lady is in Room I, then the sign on the door is true, but if a tiger is in it, the sign is false. In Room II, the situation is the opposite: a lady in the room means the sign on the door is false, and a tiger in the room means the sign is true. Again, it is possible that both rooms contain ladies or both rooms contain tigers, or that one room contains a lady and the other a tiger. The signs on the doors of the rooms are as follows:
Room1:BOTH ROOMS CONTAIN LADIES
Room2:BOTH ROOMS CONTAIN LADIES
Which door should you open (assuming, of course, that you prefer the lady to the tiger)?
Solution:
Since the signs say the same thing, they are both true or both false. Suppose they are true; then both rooms contain ladies. This would mean in particular that Room II contains a lady. But we have been told that if Room II contains a lady, the sign is false. This is a contradiction, so the signs are not true; they are both false. Therefore, Room I contains a tiger and Room II contains a lady, so you should choose Room II.
That kind of puzzles by Raymond Smullyan are my favorite, they actually have inspired me to create the puzzle machine for rooms.jmpup.com site.
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