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

Homework Help: Probability and chance of failure

  1. Mar 7, 2005 #1
    Ok, not really homework but I did not want to crowd general math.

    I have an experiment that has 96% chance of working. If I try it one hundred times what is the chance of one being a failure.

    I know with a one in two shot it is .5^2=.25 You now have a 25 percent chance of failure. Any help. Sorry at the moment my brain seems dead.
     
  2. jcsd
  3. Mar 7, 2005 #2
    Oh my God I'm an idiot. I really am more tired than this thread lets on. :zzz:
     
  4. Mar 7, 2005 #3

    Hurkyl

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Try solving the opposite problem.
     
  5. Mar 7, 2005 #4

    xanthym

    User Avatar
    Science Advisor

    Do you want the probability for "EXACTLY 1" Failure or for "AT LEAST 1" Failure?? Both can be determined from the Binomial Distribution:
    Prob{Exactly 1 Failure} = (99)*{(0.96)^(99)}*{(1 - 0.96)^(1)} =
    = (0.0696) = (6.96 %)
    Prob{At Least 1 Failure} = 1 - Prob{Exactly 0 Failures} = 1 - (0.96)^100 =
    = (0.983) = (98.3 %)


    ~~
     
    Last edited: Mar 8, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook