Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


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

Similar Threads - Probabilty reliability failure Date
B How reliable are logarithm tables? Feb 14, 2017
What is a Probabilty Density Function? Jan 27, 2015
Probabilty in a torrent (advanced probability) Feb 25, 2014
Probabilty an event will occur Sep 25, 2013
Distance probabilty question Jun 22, 2011