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Math Help - Sampling of the proportions - Question

  1. #1
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    Sampling of the proportions - Question

    According to a Gallup Poll 60%, of adults say they experience heartburn. Assume this proportion is true for the population of all adults. If a random sample of 300 adults is selected from this population, then determine the probability that:
    a) Less than 172 adults within the sample experience heatburn

    this is what I believe is:

    mean of the Sampling distrib of the proportion = .60
    standard deviation of the sampling distr of the proportion = .0283

    But I am not sure what to do after this. The answer in back of the book is .1727. I can not get that.

    Any help would greatly be appreciated.

    Thanks
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  2. #2
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    Re: Sampling of the proportions - Question

    Quote Originally Posted by onemin View Post
    According to a Gallup Poll 60%, of adults say they experience heartburn. Assume this proportion is true for the population of all adults. If a random sample of 300 adults is selected from this population, then determine the probability that:
    a) Less than 172 adults within the sample experience heatburn

    this is what I believe is:

    mean of the Sampling distrib of the proportion = .60
    standard deviation of the sampling distr of the proportion = .0283

    But I am not sure what to do after this. The answer in back of the book is .1727. I can not get that.

    Any help would greatly be appreciated.

    Thanks
    X ~ Binomial(n = 300, p = 0.6).

    Calculate Pr(X < 172).

    Normal approximation to Binomial distribution could be used.

    The book's answer is wrong.
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