The t-distribution. Use the Stata functions "ttail" and "invttail" to answer the following questions. For each question, assume that the sample size or number of observations, n, is equal to 20. (The degrees of freedom of freedom for the t- distribution is n-1.) a. P-value Pr [T-1 > 1.6] b. P-value Pr [T,_] 1.6] c. Critical value c such that Pr _ > c = 0.01 d. Critical value c such that Pr T_ c =0.01