A chemist obtained the following data for percent lindane in the triplicate analysis of an insecticide preparation: 7.23, 6.95, and 7.53. Calculate the 90% confidence interval for the mean of the three data, assuming that
(a) The only information about the precision of the method is the precision for the three analyses.
(b) On the basis of long experience with the method, it is believed that s→ σ = 0.28% lindane.