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Homework Help: Probability of picking fish from a tank

  1. Sep 10, 2012 #1
    1. The problem statement, all variables and given/known data

    a fish tank contains 12 male and 12 female guppies what is the probability that at least half of male will be selected if 15 fish are randomly selected and removed from the tank??

    2. Relevant equations

    3. The attempt at a solution
    i am tried to find the probability as following :
    P(at least 6)=P(6)+P(7)+P(8)+P(9)+P(10)+P(11)+P(12)
    =(12c6)(12c6)/(24c15) + (12c7)(12c5)/(24c15)+........+(12c12)(12c3)/(24c15)
    it seems to be a very long solution is there any way to solve it using the distribution function
  2. jcsd
  3. Sep 10, 2012 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    Re: probablity qustion

    Some problems just need a long solution; this is one of those. You ARE using the distribution function---that is exactly how you would compute it!

  4. Sep 10, 2012 #3
    Also you might want to calculate the probability that LESS than half are chosen, since
    P(0,1,2) are all zero. So you only need to calculate three values instead of 7.
  5. Sep 10, 2012 #4
    thank you very much Ray Vickson , hgfalling it really nice idea to take the complement thanks
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