error of the difference between means. (This should be the same as in part (f) of Practice Problem 2.) b. How many degrees of freedom does the t-statistic for this analysis have? c. For a 95% confidence interval, what value of a should we use? d. Using Statistical Table C, find the critical value of t for this a with the correct number of degrees of freedom. e. What is the observed difference between means (Y] - Y2)? f. Calculate the 95% confidence interval for the difference between population means