There are 4 doors to the secret Truth Club room, each one at the end of a tunnel leading there. Each of the members has a keycard to a different door. All the doors are unlocked from the inside, but to enter from the outside, one needs to swipe the door's keycard to open the door for a few seconds.

You have found a copy of one of these cards, and want to prove beyond a reasonable doubt to the club members that you can unlock one of the doors, however, you don't want to expose to anyone whose door it is. What can you do to show this? (preferably with no additional materials, and without anybody else inside the cave/tunnels)

(Assume the club members are honorable enough to follow their part of the plan you propose.)

Here is a map of the tunnels:

(In reply to What's In the Cave? by brianjn)

I appreciate your concern, but hopefully any concerns from journeymen and scholars were taken care of while this was in the queue.

"If I am to prove within a reasonable doubt that I can unlock one of the doors (and at that point none of the members need know that I have a keycard) I think it sufficient to suggest that all four doors are one-way secured, ie, I can open any from the inside and walk out."

The problem states the doors are unlocked from the inside. If you are suggesting using the items in the room, note the problem suggests you use "no additional materials"

A further note to solvers -- this problem is fairly simplistic, but I tried to include restrictions so a solution a solver would reach the idea behind the problem.

Posted by Gamer on 2008-12-27 02:05:27