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Homework Help: Conditional probability

  1. May 26, 2015 #1
    1. The problem statement, all variables and given/known data
    Profesor has 17 keys, and only one unlocks the door.
    Let random variable X be attempt at which profesor unlocks the door (key that doesnt work is saved by side)

    a) Most probable value of variable X
    b) In which attempt will profesor unlock the door
    c) Probability that he will unlock the door between (X- σ) and (X + σ)

    3. The attempt at a solution
    The most probable value is the x where p(x) is maximum.
    How should i find it here? To find maximum i need some type of distribution.
    b) This follows after i solve a)
  2. jcsd
  3. May 26, 2015 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    PF rules require you to show some effort at solving the problem.

    You need to determine the probabilities ##P(X = 1), P(X = 2), \ldots##, etc. So, to say that the event ##\{X =1\}## occurs, what must happen when the professor selects keys? What is that event's probability? To say that the event ##\{ X = 2\}## occurs, what must happen when the professor selects keys? What would be the probability of that event?

    Keep going like that.
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