Problem:

Assume a sample of 10 modules was selected for analysis from a 
new software release. The mean development effort per module is 
found to be 28 man days with a standard deviation of 6 man days.

Construct and interpret a 95% confidence interval for the mean 
development effort per module for the release.

Solution:

Since the sample size is small we must assume that development effort
is normally distributed and so the t table will be required. Also
s(ybar) is 6/sqrt(9)=6/3=2. Since the required t value is 2.26 then 
the 95% CI is:
                     28 plus/minus 2.26*2 
                     28 plus/minus 4.52
                         [23.48, 32.52]

That is, you are 95% confident that mu(y) is between [23.48, 32.52].