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Thread: A probability problem

  1. #1
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    A probability problem




    Hi all,
    I would like to solve the problem bellow. To some it might seem to eassy. However i would appreciate some hints.
    Thanks in advance ...

    here is the statement:

    "A new ornament has been released by a manufacturer. They made 1000 of the ornaments in total, but 350 were made from glass and the rest were made from clay. The ornaments are sold in a sealed box, so when buying the ornament it is not possible to tell whether you have a glass or a clay edition. Upon an impact, the glass ornaments have a 9/10 probability of breakin, and the clay ornaments have a 2/10 probability of breaking. To resell a broken ornament is worth nothing regardless of what is made of, a glass ornament is worth 100 and the clay ornament is worth 10. You just bought an ornament, but than dropped it before you could see what is made of. What is the expected value of your ornament now?"

  2. #2
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    Re: A probability problem

    Now, before gettin further i would like to post what i have understood...
    once again please correct me where i m wrong
    thanks
    ____________

    i think that we should find the probabiliti of the ornament of being broken.
    it means that a 'logical' approach could sound like this:

    Pb<=>(P_glass and P_glass_b) or (P_clay and P_clay_b)
    where
    Pb is the probability of the ornament to be broken
    P_glass - probability that the ornament to be made out of glass
    P_glass_b - probability of the glass ornament to be broken
    and so on

    =>
    Pb = (.35*.9)+(.65*.2)=.45

    so the probability of the ornament to be broken is about 45%.
    what i need to know is, how do you translate that into the expected value?

  3. #3
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    Re: A probability problem

    You should know that there are 4 scenarios, and each scenario will have its corresponding reselling value. Then you can calculate the probability of each scenario happening, and apply the formula of expected value to calculate it.

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    Re: A probability problem

    what would be the expected value formula?

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    Re: A probability problem

    So have you learn the formula calculating the expected value of a discrete random variable (the reselling value)?

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    Re: A probability problem

    no, i have no ideea how to calculate that or where to get it from
    Last edited by marius15; 04-26-2015 at 01:38 PM.

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    Re: A probability problem

    http://en.wikipedia.org/wiki/Expecte...2C_finite_case

    If you really do not know anything about expected value, I suggest you to take a look with those introductory probability materials first before you move on. This is the basic background knowledge required for this question and for most of the probability questions, we assume you already familiar with this. So there will be a problem if you miss this important part in your study process.

  8. The Following User Says Thank You to BGM For This Useful Post:

    marius15 (04-26-2015)

  9. #8
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    Re: A probability problem


    thanks
    it was really usefull

    so the expected value is:
    E = value_of_unbroken_clay_orn*(Probability_that_unbroken_clay_orn_occur)+value_of_broken_clay_orn*(Probability_that_unbroken_clay_orn_occur)+
    +value_of_unbroken_glass_orn*(Probability_that_unbroken_glass_orn_occur)+value_of_broken_glass_orn*(Probability_that_unbroken_glass_orn_occur)

    =>

    E = 10*(.65*.8) + 0*(.65*.2) + 100*(.35*.1) + 0*(.35*.9) = 8.7

    thanks again for the hints

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