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Math Help - Probabilities

  1. #1
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    Probabilities

    1. As accounts manager in your company, you classify 60% of your customers as "good credit" and the rest as "risky credit" depending on their credit rating. Customers in the "risky" category allow their accounts to go overdue 70% of the time on average, whereas those in the "good" category allow their accounts to become overdue only 20% of the time.

    What percentage of overdue accounts are held by customers in the "risky credit" category?



    2. A batch of fifty items is inspected by testing three items selected without replacement. If one of the three is defective, the batch is rejected. What is the probability that the batch is accepted if it contains five defectives?


    OK could someone help out a little bit my brain is failing to work, I have done some working out but none of it seems to make sense and it seems easy. Don't know what's going on up there.
    Last edited by mr fantastic; December 15th 2009 at 06:41 PM. Reason: Moved some questions to a new thread
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  2. #2
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    2. A batch of fifty items is inspected by testing three items selected without replacement. If one of the three is defective, the batch is rejected. What is the probability that the batch is accepted if it contains fi ve defectives?
    In order to be accepted, you have to choose no defects out of the batch.
    There are 45 good ones and 5 rejects. So, you have to choose 3 from the 45 good ones and 0 from the 5 bad ones.

    \frac{\binom{45}{3}\cdot \binom{5}{0}}{\binom{50}{3}}
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    hi thanks for your help. I get an unusual answer from this
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  4. #4
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    It turns out ot be \frac{1419}{1960}\approx .724

    I see nothing unusual.
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