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Probability distribution pin code guessing

  1. Mar 7, 2012 #1
    1. The problem statement, all variables and given/known data
    What is the distribution of stochastic variable X = "the number of attempts needed to find the correct last digit of a pin code"


    2. Relevant equations



    3. The attempt at a solution
    I thought it was like this:
    P(X=1) = 1/10
    P(X=2) = 9/10*1/9
    P(X=3) = 9/10*8/9*1/7
    ...
    ...
    P(X=10) = 9/10*8/9*7/8*6/7*5/6*4/5*3/4*2/3*1/2*1

    Thank you!
     
  2. jcsd
  3. Mar 7, 2012 #2

    Ray Vickson

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    Re: Probability_distribution_pin_code_guessing

    Looks good.

    RGV
     
  4. Mar 7, 2012 #3
    Re: Probability_distribution_pin_code_guessing

    Thanks. Is it possible to capture P(X=x) in a formula?
     
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