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Math Help - conditional probability problem

  1. #1
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    conditional probability problem

    1. The problem statement, all variables and given/known data


    I've spent a few hours but unable to work out the solution of the following questions successfully.


    The question is as follows:



    I am having problems with (a)(iii) and (b)(ii)






    My attempts were as follows which were unsuccessful....






    (a)(iii) Although I can work out the solution at last, my original attempt was incorrect but I don't understand why.


    My first attempt:
    P(pass) = P(4 answer correct) + P(5 answer correct) + P(all answer correct)
    = (3x3x1x1x1x1)/(6x6x6x6x6x6) + (3x1x1x1x1x1)/(6x6x6x6x6x6) + (1x1x1x1x1x1)/(6x6x6x6x6x6)


    However, this is wrong. But I don't understand why............


    (b)(iii) I can't work out the solution at all. Please help. Thank you.
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  2. #2
    Senior Member
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    Re: conditional probability problem

    If guessing probability of getting a question correct =1/4
    So this is the binomial distribution B(6,1/4)
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