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Homework Help: Estimate exponential distribution parameter

  1. Sep 12, 2013 #1
    1. The problem statement, all variables and given/known data

    A certain type of transistor has an exponentially distributed time of operation. After testing 400 transistors, it is observed that after one time unit, only 109 transistors are working.

    Estimate the expected time of operation.

    2. Relevant equations

    3. The attempt at a solution

    It was suggested that I approximate with

    X ≈ Bin(400,p)

    Then conclude that p can be estimated with p* = 109/401 = e-1/μ

    That part I don't get is: why is p = e-1/μ ?
  2. jcsd
  3. Sep 12, 2013 #2


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    2017 Award

    Staff: Mentor

    In an exponential distribution, what is the probability that something survives for a time t? Then set t=1.
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