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Math Help - statistics confidence intervals

  1. #1
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    statistics confidence intervals

    so so confused. had to miss a week of class. any guidance is greatly appreciated.

    a random sample of 121 checing accounts at a bank showed an average daily balance of $280. the standard deviation of the population is known to be $66

    a) is it necessary to know anything about the shape of the distribution of the account balances in order to make an interval estimate of the mean of all the account balances? explain
    b) find the standard error of the mean
    c) give a point estimate of the population mean
    d) determine the margin of error for a 95% confidence interval
    e) construct a 95% confidence interval for the mean
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  2. #2
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    Hi there JGaraffa,

    Have you thought about this problem yet? Have you attempted these? Have you any class note you can refer to?
    Quote Originally Posted by JGaraffa View Post

    a) is it necessary to know anything about the shape of the distribution of the account balances in order to make an interval estimate of the mean of all the account balances? explain
    What data distributions do you know? What does this mean here?


    Quote Originally Posted by JGaraffa View Post


    b) find the standard error of the mean
    This is an pretty easy one, \displaystyle  SE = \frac{\sigma}{\sqrt{n}} or \displaystyle  SE = \frac{s}{\sqrt{n}}

    Which one to use in your case? and why?


    Quote Originally Posted by JGaraffa View Post


    c) give a point estimate of the population mean
    Will be the same as the sample mean




    Quote Originally Posted by JGaraffa View Post

    e) construct a 95% confidence interval for the mean
    Try  \displaystyle \bar{x}\pm Z_{0.95}\times SE
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