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Math Help - picking batteries

  1. #1
    Junior Member elenaas's Avatar
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    picking batteries

    A box contains a dozen old baterries, five of which are tottaly dead. You start picking batteries one at a time and testing them. Find the probabilities:
    a. The first two you choose are both good.
    b. At least one of the first three works.
    c. The first four you pick all work.
    d. You have to pick 5 batteries in order to find one that works.

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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by elenaas View Post
    A box contains a dozen old baterries, five of which are tottaly dead. You start picking batteries one at a time and testing them. Find the probabilities:
    a. The first two you choose are both good.
    What is the probability that the first id good.

    If the first was good what is the probability that the second is good?

    The probability you seek is the product of these.

    CB
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