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Homework Help: Probability when seleting balls from an urn

  1. May 18, 2010 #1
    1. The problem statement, all variables and given/known data

    There is total of 300 balls in the basket, 30 of them is red (rest is white). If we picked up, randomly, 4 balls, what is the probabilty that all of them is red ?


    2. The attempt at a solution

    For one picked ball, probability that it's red is 30/300 = 1/10.
    If picked ball is red, probabilty for next ball is 29/299,and so on, 28/298, 27/297.

    Is that correct ? And, what next ?
     
  2. jcsd
  3. May 18, 2010 #2
    Re: Probability


    Yup, thats right so far.
    In probability, what is the relationship with "And" events? :wink:
     
  4. May 18, 2010 #3
    Re: Probability

    P(A and B) = P(A) x P(B) ???
     
  5. May 18, 2010 #4
    Re: Probability

    P(A and B) = P(A) x P(B after A) is correct,because this is depended events, is that true ?

    If it is, the solution would be: 30/300 * 29/299 * 28/298 * 27/297.
     
  6. May 18, 2010 #5
    Re: Probability

    Exactly. :smile:
     
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