4 thoughts on “Unwrite – 2

  1. There are 8 floors in a building excluding ground floor. 4 people get in the lift along with Mr X on ground floor. Given that each person get off the lift on a different floor, what is the probability that Mr X gets off the lift before exactly 3 people?

  2. Not clear with the explanation for the 5th question, can you please explain a bit further? I can solve it by the traditional method but would like to explore more of this symmetry thing for knowledge,hence asking.

    • Probability of 3 heads = Probability of 3 tails (which is 2 heads).
      Probability of 4 heads = Probability of 4 tails (which is 1 head).
      Probability of 5 heads = Probability of 5 tails (which is 0 heads).

      Now think 🙂


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