The following data resulted from 15 independent measurements of the melting point of lead. 322.3 339.1 323.3 330.8 328.4 323.2 338.3 324.2 334.9 328.2 329.4 329.5 328.2 339.7 326.5 Assuming that the measurements can be regarded as constituting a normal sample whose mean is the true melting point of lead, determine a 95% confidence interval for this value.