(a) Determine the critical value for a right-tailed test of a population mean at the α = 0.01 level of significance with 15 degrees of freedom.
(b) Determine the critical value for a left-tailed test of a population mean at the α = 0.05 level of significance based on a sample size of n = 20.
(c) Determine the critical values for a two-tailed test of a population mean at the α = 0.05 level of significance based on a sample size of n = 13.