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Exponential distribution word problem

  1. Dec 25, 2012 #1
    The Information Systems Audit and Control Association surveyed office workers to learn about the anticipated usage of office computers for holiday shopping. Assume that the number of hours a worker spends doing holiday shopping on an office computer follows an exponential distribution.

    a) The study reported that there is a .53 probability that a worker uses the office computer for holiday shopping 5 hours or less. Is the mean time spent using an office computer for holiday shopping closest to 5.8,6.2,6.6, or 7 hours?

    b) Using the mean time from part a), whats the probability that a worker uses the office computer for holiday shopping more than 10 hours?

    c) What is the probability that a worker uses the office computer fr holiday shopping between 4 and 8 hours?

    I just dont know how to calculate the mean. Once i get that I'll be able to do parts b) and c). Any help with part a) will be very helpful.thanks!
     
  2. jcsd
  3. Dec 26, 2012 #2

    Simon Bridge

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    Do you know the general form of the exponential distribution?
     
  4. Dec 26, 2012 #3
    f(x)= 1/a (e)^ -x/a
    where a is the mean?
     
  5. Dec 28, 2012 #4

    Simon Bridge

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    Good. In terms of time, you may prefer: $$p(t)=\frac{1}{\tau}e^{t/\tau}$$... where ##\tau## is the mean.

    Can you turn that into an expression for the probability that the time is less than some specified value T : $$p(t<T)=\cdots$$
     
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