Suppose that when sampling from a normal population having an unknown mean μ and unknown variance σ 2, we wish to determine a sample size n so as to guarantee that the resulting 100(1 - α) percent confidence interval for μ will be of size no greater than A, for given values α and A. Explain how we can approxi- mately do this by a double sampling scheme that first takes a subsample of size 30 and then chooses the total sample size by using the results of the first subsample.