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Math Help - Second and Final Probability question.

  1. #1
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    Second and Final Probability question.

    For this question, I tried it using P(x success)=_{n}C_{k}P^k(1-P)^{n-k}, but It doesn't feel right. and I'm not getting the correct answer, I think I just need a push in the right direction on this one.

    The probability of exactly 4 out of 10 people having a red ticket at a charity ball is aproximately 0.2508. What is the probability, as a percentage, of a random person having a red ticket? Round your answer to the nearest percent. (HINT: Red or Not Red.)
    Am I supposed to set P(xsuccess)=0.2508 and solve backwards? I tried plugging 0.2508 as P in the above formula and solving, but that was more of a wild shot.

    I'm not sure where to go with this one. =/ Any help would be appreciated!
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  2. #2
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    Probability

    Hello Kasper
    Quote Originally Posted by Kasper View Post
    For this question, I tried it using P(x success)=_{n}C_{k}P^k(1-P)^{n-k}, but It doesn't feel right. and I'm not getting the correct answer, I think I just need a push in the right direction on this one.



    Am I supposed to set P(xsuccess)=0.2508 and solve backwards? I tried plugging 0.2508 as P in the above formula and solving, but that was more of a wild shot.

    I'm not sure where to go with this one. =/ Any help would be appreciated!
    Your approach is the only one I can think of. But you get an equation that looks pretty well impossible to solve: \binom{10}{4}p^4(1-p)^6 = 0.2508.

    I have got an answer, though. It's p = 0.4. But I cheated, and used an Excel spreadsheet!

    Grandad
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  3. #3
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    Quote Originally Posted by Grandad View Post
    Hello KasperYour approach is the only one I can think of. But you get an equation that looks pretty well impossible to solve: \binom{10}{4}p^4(1-p)^6 = 0.2508.

    I have got an answer, though. It's p = 0.4. But I cheated, and used an Excel spreadsheet!

    Grandad
    I suspect that access to appropriate technology was assumed by whoever who wrote the question.

    The question should also have stated the required accuracy for the answer. Otherwise there's an implication that an exact answer is required (and obviously I doubt very much that an exact answer is required).

    Sorry Grandad, 0.4 looks too misleadingly exact for my liking .... The answer is p = 0.4021, correct to four decimal places and courtesy of my TI-89.
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