1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted