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    queeninurse's Avatar
    queeninurse Posts: 1, Reputation: 1
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    #1

    Jul 1, 2008, 01:30 PM
    Finding confidence interval
    A machine produces 3 inch nails. A sample of 100 nails is selected, and it is found that 25 are shorter than 3 inches. Find a 95% confidence interval on the proportion of all such nails that are shorter than 3 inches
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Jul 1, 2008, 02:19 PM
    p=.25 because 25/100 = .25

    Therefore, q=1-p=.75

    The error of estimate is given by the formula:



    The z score for 95% CI is z=1.96.

    Now, plug your values into the formula.

    Add and subtract that value from .25 to create your confidence interval.

    It should be written as
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