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Homework Help: Statistics Probability

  1. Feb 15, 2012 #1
    A1 Computer has 15 tablets stocked, but four of them were actually defectives.
    A client bought two tablets from A1 Computer. If both of them are good, things are fi ne.
    If the client gets one defective machine, A1 Computer will replace it and give a $100 rebate
    to the client. If the clients gets two defective machines, A1 Computer will replace both of
    them and give a $1000 rebate to the client. What is the expected value and the standard
    deviation of the company's rebate?

    P(R) = 4/15 x 100 = 26.6%

    Since there were 4 defective machines then 2 x 1000 = 2000 was given away to client(s)
    so value = 2000
    how would I find the standard deviation? I know the usual formula but where would i plug into it?
  2. jcsd
  3. Feb 15, 2012 #2


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    Science Advisor

    I think you are completely misunderstanding the problem.

    You calculated P(R), the probability that a given computer is bad. Now What is the probability that, of 2 computers chosen at random from those 15
    1) neither is bad.
    2) one is bad.
    3) both are bad.
    Last edited by a moderator: Feb 15, 2012
  4. Feb 15, 2012 #3

    Ray Vickson

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    Science Advisor
    Homework Helper

    I don't understand. If you know the formula, what is preventing you from substituting in the appropriate numbers and doing the arithmetic? Or, are you saying that you don't know what numbers to plug in?

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