"Radford Neal" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > In article <[EMAIL PROTECTED]>, > Jo <[EMAIL PROTECTED]> wrote: > > >The time that students spend at part time jobs per week is approximately > >Normally distributed with standard deviation 8 hours. A random sample of 130 > >students is taken and the sample mean is 11.4 hours. > > > >How do I find the 90% lower confidence limit for the true mean (mu)? > > You don't, since the assumptions stated are false. It's not possible > for the time to have a mean of around 11 and standard deviation of 8, > since that would produce substantial numbers of students who work for > a negative number of hours, which is clearly impossible.
That would be about 8% of the students working negative times. Perhaps that's why they used the word *approximately*. Or perhaps the variance is meant to be 8 hours^2 ;-) Dirk Vdm . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
