finding standard deviation ?

**kscheels** · July 19th 2008, 06:30 PM

GIven confidence level,11.24<u<12.01 and that n=90 + c= .90, find the sample standard devaiton o

**kscheels** · July 19th 2008, 06:31 PM

[quote=kscheels;168572]GIven confidence level,11.24<u<12.01 and that n=90 + c= .90, find the sample standard devaiton o.

**mr fantastic** · July 19th 2008, 08:35 PM

Originally Posted by kscheels

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.

Thread: finding standard deviation ?

LinkBack

Thread Tools

Display

finding standard deviation ?

Similar Math Help Forum Discussions

Finding mean, variance and standard deviation.

Finding Standard deviation and mean value after finding z curve areas

Finding standard deviation and mean

Finding a standard deviation from a set of averages and standard deviations

Finding the standard deviation

Search Tags