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Math Help - finding standard deviation ?

  1. #1
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    finding standard deviation ?

    GIven confidence level,11.24<u<12.01 and that n=90 + c= .90, find the sample standard devaiton o
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    [quote=kscheels;168572]GIven confidence level,11.24<u<12.01 and that n=90 + c= .90, find the sample standard devaiton o.
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    Quote Originally Posted by kscheels View Post
    GIven confidence level,11.24<u<12.01 and that n=90 + c= .90, find the sample standard devaiton o
    I'm assuming that since you ask for sample standard deviation rather than population standard deviation, the confidence interval has been constructed using the t-distribution:

    L_1 = \bar{x} - \frac{s}{\sqrt{n}} \, t_{n-1, \, \alpha/2} < \mu < \bar{x} + \frac{s}{\sqrt{n}} \, t_{n-1, \, \alpha/2} = L_2


    Therefore L_2 - L_1 = \frac{2 s}{\sqrt{n}} \, t_{n-1, ~ \alpha/2}.

    In your case \alpha = 0.1 \Rightarrow \frac{\alpha}{2} = 0.05 (I think ..... it's not really clear from what you posted), n = 90, L_1 = 11.24 and L_2 = 12.01. Use a table of critical values to get t_{89, ~ 0.05}.

    Substitute all these values and solve for s.
    Last edited by mr fantastic; July 19th 2008 at 08:46 PM.
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