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Math Help - Probability distribution of X

  1. #1
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    Probability distribution of X

    A box conains 8 tickets. Two are marked 1, two marked 2, two marked 3, and two marked 4. Tickets are drawn at random from the box without replacement until a number appears that has appeared before. Let X be the number of draws that are made. Make a table to display the probability distribution of X.

    Only part of the answer is given, P(x=2) = 5/35. Ive been trying to figure out how they got this ... where does the 35 come from?
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  2. #2
    Moo
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    Hello,

    P(X=2) means that you draw the same number during the first two drawings.
    So the first draw will give a number a, the second draw will give the second number a.
    Whatever the first number is, the second has to be the same... so among the 7 remaining tickets, you have to pick a specific ticket.
    So the probability will be 1/7

    But maybe they want you to have a different reasoning... Like thinking with combinations or arrangements.
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