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Determining the number of one hat

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N people team up and decide on a strategy for playing this game.  Then they walk into a room.  On entry to the room, each person is given a hat on which one of the first N natural numbers is written.  There may be duplicate hat numbers.  For example, for N=3, the 3 team members may get hats labeled 2, 0, 2.  Each person can see the numbers written on the others’ hats, but does not know the number written on his own hat.  Every person then simultaneously guesses the number of his own hat.  What strategy can the team follow to make sure that at least one person on the team guesses his hat number correctly?

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ronret45 Expert Asked on 1st August 2015 in Microsoft Interview Puzzles.
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    • 1 Answer(s)

    The first person adds all the numbers he sees and tells it out loud.

    Now the second person, will ignore the number on the first person’s hat. He will add all the other numbers he sees( he won’t include his and the first person’s number). He will subtract what he got from what the first person announced. All the other persons will do the same thing. They’ll ignore the first person’s number.
    This way everyone, other than the first person says the correct number.

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    GeNiUs Genius Answered on 5th December 2015.

    kjscola

    But the puzzle says they all have to guess simultaneously, so the other players can’t use the first person’s guess to figure out their answer.

    on 27th August 2017.
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