Here is a riddle I made up. There are a few solutions, the most simple and elegant was offered by a good friend. Good luck!
A man is seleceted by an evil villain and
sat at a table where he will be forced to play a game. If victorious, the
villain will release his hostage daughter and the family may go on with
their normal life. Failure will result in a lifetime of bondage for his
loved
one. The villain first blindfolds the man, so he is unable to see. He
then places 9 coins in front of the man, each facing either heads up or
tales up. The villain then says to the man:
"If you can point to each coin, one by one, and tell me whether that coin
is tales up or heads up, then your daughter is free. Make one mistake,
and she is mine forever."
The man replies hastily:
"But that is impossible! How can I possibly know if the coins are heads
up or tales up with my eyes blindfolded?!"
"Ah," replies the villain, "herein lies the game. For I will give you 8
questions that you may ask me, each time you are guarenteed that I will
answer with the truth. However, my answers will only be 'Yes' or 'No', so
you must ask your questions accodingly. The 8 answers to your eight
questions will be the only information you may obtain."
"That's still not fair!" the man insists. "There are 9 coins and only 8
questions, how will I know the state of the last coin?"
"I will give you one last clue," the villain responds. "The majority of
the coins are facing tales up."
Can the man save his daughter, regardless of how the villain arranges the
coins?