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Math Help - sample size, sampling error

  1. #1
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    Exclamation sample size, sampling error

    could someone please explain the concept of sampling error? i can't really find it in my text book
    ahh thanks
    also i am stuck on two more problems. (last ones, i swear! haha)

    st dev=1200
    want a 95% confidence interval for the population value of annual telephone expenditure with an error of estimation (sampling error) no greater than $50
    what sample size should be used?

    suppose that we want a 95% confidence interval for the population value of annual telephone expenditure that is no wider than $100
    what sample size should be used?
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  2. #2
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    Quote Originally Posted by lalalamaths View Post
    [snip]
    st dev=1200
    want a 95% confidence interval for the population value of annual telephone expenditure with an error of estimation (sampling error) no greater than $50
    what sample size should be used?

    [snip]
    Assuming a normal distribution, solve z_{\alpha/2} \cdot \frac{\sigma}{n} = 50 for n where the other symbols have the usual meaning and you've been given their values.
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