Man on a Plane Probability (in the wild)

My friend had an interview with Google during which they asked him this interesting question:
A man gets on a plane with n seats, but he has lost his ticket. So this man randomly chooses a seat. The next guy gets on the plane with his ticket. He goes to his seat, if it is empty, he sits there. If it is taken, he randomly chooses a seat. This continues until n-1 seats are filled. The n-th person enters the plane with his ticket. He goes to his seat. What is the probability that it is empty?



Posted on September 7, 2009, in Uncategorized. Bookmark the permalink. 2 Comments.

  1. Did your friend get it right?
    That’s quite a tough one for them to throw at you

    • He eventually got it right, but he had to work it out. And of course this was all in the middle of several hours of interviews, after which, they wanted to hire him but couldn’t because that department was on a hiring freeze.

      But don’t feel too bad for him. He is making a ton of money in a post-doc position at IBM.

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