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    jo1na85's Avatar
    jo1na85 Posts: 1, Reputation: 1
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    #1

    Mar 6, 2009, 07:35 PM
    Confidence Intervals
    First time here, but really need help with a statistic problem, hoping someone can really help.

    The question is: A utility company has 80K customers. It hires a market research firm to randomly sample 1K households and to estimate the average amount of insulation in the 80K customers home. The average amt of insulation in the sample of household is 12inches. The sample standard deviation is 15 inches. Set up and interpret and a 95% confidence interval. (use 1.96 for the z-value)


    Thanks:confused:
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Mar 7, 2009, 07:47 AM
    Just use the formula:



    Where

    Add it to and subtract it from the sample mean.

    You want

    Therefore, you can say with 95% confidence that the populations mean falls in that range.
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