A random sample of n measurements was selected from a population with standard deviation = 19.4 and unknown mean . Calculate a 90% confidence interval for for each of the following situa"
a) ± 2.145(19.4/√n)
b) ± 1.645(19.4/√n)
c) ± 1.960(19.4/√n)
d) ± 2.326(19.4/√n)