2 oints eBook Print References Consider the following data drawn independently from normally distributed populations: (You may find it useful to reference the appropriate table: z table or t table) X1 = -18.1 $1 = 8.2 71 = 13 a. Construct the 99% confidence interval for the difference between the population means. Assume the population variances are unknown but equal. (Round all intermediate calculations to at least 4 decimal places and final answers to 2 decimal places.) Confidence interval is X2 = -17.0 52 = 8.7 n2 = 13 to b. Specify the competing hypotheses in order to determine whether or not the population means differ. Ho: H1 H2 = 0; HA: H1 H2 * 0 Ho: H1 H2 0; HA: H1 - H2 < 0 - Ho: H1 H2 0; HA: H1 - H2 > 0