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Altered die problem (Probability)

  1. Oct 11, 2006 #1
    Hello everyone,

    I need some help with the following prob:

    A bag contains 3 dice, 2 fair and 1 altered with all odd numbers replace with "1". One die is randomly selected and rolled independently twice. If the outcomes of both rolls were "1" and "1", what is the prob that the selected die is the altered die?

  2. jcsd
  3. Oct 11, 2006 #2


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    What have you done?
  4. Oct 11, 2006 #3


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    What is the probability of rolling "1" two times in a row with a regular die? What is the probability of rolling "1" two times in a row with an altered die?
  5. Oct 11, 2006 #4
    Altere die problem

    Here's what I've done:

    Let A= Altered die and B=outcome is 1

    then P(A|B) = P(A∩B)/ P(B)
    P(A∩B) = 1/12 ( outcome of 3 11's)
    P(B)= 5/9 ( total outcome of 1's)

    therefore P(A|B) = (1/12)/(5/9) = 3/20

    Is this correct? Is there another way to approach this problem?

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