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Math Help - simple binomial distribution problem?

  1. #1
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    simple binomial distribution problem?

    Given the random variable X such that X ~ B(7, p) and P(X = 4) = 0.09724, find P (X = 2) where p < 0.5.

    It seems to be so simple, but the solution eludes me
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  3. #3
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    Quote Originally Posted by mirajshah View Post
    Given the random variable X such that X ~ B(7, p) and P(X = 4) = 0.09724, find P (X = 2) where p < 0.5.

    It seems to be so simple, but the solution eludes me
    Since P(X=4)=0.09724 we have:

    P(X=4)=\dfrac{7!}{4!3!}p^4(1-p)^3=0.09724

    Now you need to find p<0.5 that satisfies this equation. Probably the best approach is to find a numerical solution (trial and error, graphical method or the bisection method will do, and indicates a solution close to p=0.3)

    Now you only need to evaluate P(X=2)=b(2;7,0.3)
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    Quote Originally Posted by stebko View Post
    0,317652
    Not only useless (because no explanation) but wrong

    CB
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