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:
Club members should stay outside the main entrance of the cave/tunnels until I'm inside the Truth Club Room not to see which is the tunnel/door I used to enter.
Once I'm in (eg after the time the above step requires) they should
take position at the entrances of the tunnels.
I just need to open more than one door (at least 2, even at different times) and shout to demonstrate to the club members that I've access to the room. If I wasn't inside they could only hear my voice comes from one tunnel only.
Posted by Marco
on 2014-08-08 10:09:20