Ferric chloride is used as a flux in some types of
extraction metallurgy processes. This material is
shipped in containers, and the container weight
varies. It is important to obtain an accurate estimate
of mean container weight. Suppose that from long
experience a reliable value for the standard deviation
of flux container weight is determined to be 4 lb.
How large a sample would be required to construct a
95% two-sided confidence interval on the mean that
has a total width of 1 lb?