Let /12 represent the population mean cotinine level 12 hours after smoking the cig- arette and /24 the mean cotinine level 24 hours after smoking. It is believed that: M24 must be lower than /12. (a) Construct a one-sided 95% confidence interval for the true difference in pop- ulation means /412 - /24. (b) Test the null hypothesis that the population means are identical at the a = 0.05 level of significance. What do you conclude? Question 4: Exercise 10 on page 280 in the textbook. As part of the Women's Health Trial, one group of women were encouraged to adopt a low-fat diet while a second group received no dietary counseling. A year later, the women in the intervention group had successfully maintained their diets. At that time, a study was undertaken to determine whether their husbands also had a reduced level of fat intake. (a) In the intervention group, a sample of 156 husbands has mean daily fat intake X1 = 54.8 grams and standard deviation S1 = 28.1 grams. In the control group, a sample of 148 husbands has mean intake x2 = 69.5 grams and standard deviation S2 = 34.7 grams. Calculate separate 95% confidence intervals for the true mean fat intakes of men in each group. (b) Formally test the null hypothesis that the two groups of men have the same mean dietary fat intake using a two-sided test. What do you conclude? (c) Construct a 95% confidence interval for the true difference in population means