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: A car's odometer shows 72927 miles, a palindromic number. What are the minimum miles you would need to travel to form another? (a palindrome can be read both forwards and backwards, like "Kayak")
Riddle: A horse travels a certain distance each day. Strangely enough, two of its legs travel 30 miles each day and the other two legs travel nearly 31 miles. It would seem that two of the horse's legs must be one mile ahead of the other two legs, but of course, this can't be true, since the horse is normal. How is this possible?
Answer: The horse operates a mill and travels in a circular clockwise direction. The two outside legs will travel a greater distance than the two inside legs.