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Probabilty of reliability and the failure rate

  1. Sep 8, 2006 #1
    I am currently studying for a business qualification I am stumbling over a question.

    It concerns calculating failure rate. The equation I know for this involves knowing the number of failures over a given time.

    However the question is: "A device has a reliability of 0.8 over 2000 hours, calculate the failure rate."

    How can I firstly work out the number of failures from this? It doesn't give any other information, ie total sample size etc. just the reliability over 2000 hours.

    It's a bit of a killer as the next questions refer to MTBF (mean time between failures) and MTTF (mean time to failure) but I need to know the failure rate first before I can tackle these questions which I am confident in answering once the failure rate has been determined.

  2. jcsd
  3. Sep 8, 2006 #2


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    Science Advisor

    You are probably meant to assume an exponential probabilty density model. The data "A device has a reliability of 0.8 over 2000 hours" will let you calculate the single constant in the model and everything else should follow from that.

    That is, 0.8 = exp(-2000 k). Solve this for "k".
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