Riddle: Suppose you want to send in the mail a valuable object to a friend. You have a box which is big enough to hold the object. The box has a locking ring which is large enough to have a lock attached and you have several locks with keys. However, your friend does not have the key to any lock that you have. You cannot send the key in an unlocked box since it may be stolen or copied. How do you send the valuable object, locked, to your friend - so it may be opened by your friend?
Answer: Send the box with a lock attached and locked. Your friend attaches his or her own lock and sends the box back to you. You remove your lock and send it back to your friend. Your friend may then remove the lock she or he put on and open the box.
Riddle: If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?
Answer: You will never reach the door! If you only move half the distance, then you will always have half the distance remaining no matter how small the number.
Riddle: A traveler, on his way to Miami, reaches a road junction, where he can turn left or right. He knows that only one of the two roads leads to Miami, but unfortunately, he does not know which one. Fortunately, he sees two twin brothers standing at the road junction, and he decides to ask them for directions. The traveler knows that one of the two brothers always tells the truth and the other one always lies. Unfortunately, he does not know which one always tells the truth and which one always lies. How can the traveler find out the way to Miami by asking just one question to one of the two brothers?
Answer: The question that the traveler should ask is: "Does the left road lead to Miami according to your brother?" If the answer is "Yes", the traveler should turn right, and if the answer is "No", the traveler should turn left.