Hat Trick
Braingle.com
The Situation:
There is an island with 10 inhabitants. One day a
monster comes and says that he intends to eat every one of them but
will give them a chance to survive in the following way:
In the morning, the monster will line up all the people - single file
so that the last person sees the remaining 9, the next person sees the
remaining 8, and so on until the first person that obviously sees no
one in front of himself. The monster will then place black or white
hats on their heads randomly (they can be all white, all black or any
combination thereof).
The monster will offer each person starting with the last one (who
sees everyone else's hats) to guess the color of his/her own hat. The
answer can only be one word: "white" or "black". The monster will eat
him on the spot if he guessed wrong, and will leave him alive if he
guessed right. All the remaining people will hear both the guess and
the outcome of the guess. The monster will then go on to the next to
last person (who only sees 8 people), and so on until the end.
The monster gives them the whole night to think.
The Task:
Devise the optimal strategy that these poor natives
could use to maximize their survival rate.
Assumptions:
1) All the 10 people can easily understand your
strategy, and will execute it with perfect precision.
2) If the
monster suspects that any of the people are giving away information to
any of the remaining team members by intonation of words when
answering, or any other signs, or by touch, he will eat everyone.
3) The only allowed response is a short, unemotional "white" or
"black".
4) Having said that, I will add that you can put any
value you like into each of these words. For example, "white" can mean
"my mother did my laundry" and "black" can mean the guy in front of me
is wearing a black hat.
Today's brain teaser courtesy of Braingle.com.
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