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According to a Harris Interactive poll conducted in 2009, 20% of American adults smoke. In a random sample of 500 American adults, what is the probability that no more than 100 smoke?

  • statistics -

    Find mean and standard deviation.

    mean = np = (500)(.20) = ?
    standard deviation = √npq = √(500)(.20)(.80) = ?

    Note: q = 1 - p

    Once you have calculated the mean and standard deviation above, use z-scores to find the probability:

    z = (x - mean)/sd

    Use 100 for x.

    After you find the z-score, check a z-table to determine your probability.

    I hope this will help get you started.

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