University Variety 1 2 3 4 5 6 7 8 9 1 38 23 35 41 44 29 37 31 38 2 45 25 31 38 50 33 36 40 43 Find a 95% confidence interval for the mean difference between the vields of the two varieties, assuming the differences of yields to be approximately normally dis- tributed. Explain why pairing is necessary in this prob- lem. 9.46 The following data represent the running times of films produced by two motion-picture companies. Company Time (minutes) I 103 94 110 87 98 IT 97 82 123 92 175 88 118 Compute a 90% confidence interval for the difference between the average running times of films produced by the two companies. Assume that the running-time dif- ferences are approximately normally distributed with unequal variances