11.1 A study made by a staff officer of an armored division showed that in a random sample of n = 40 days the division had on the average 1,126 vehicles in operating condition. Given that o = 135 for such data, what can this officer assert with 95% confidence about the maximum error if he uses x = 1,126 as an estimate of the actual daily average number of vehicles that this armored division has in operating condition? 11.2 With reference to Exercise 11.1, construct a 99% confidence interval for the actual average daily number of vehicles that this armored division has in operating condition. 11.3 A study of the annual growth of a certain kind of orchid showed that (under controlled conditions) a random sample of n = 40 of these orchids grew on the average 32.5 mm per year. Given that o = 3.2 mm for such data, what can one conclude with 99% confidence about the maximum error if x = 32.5 mm is used as an estimate of the true average annual growth of this kind of orchid (under the given controlled conditions)? 11.4 With reference to Exercise 11.3, construct a 98% confidence interval for the true average annual growth of this kind of orchid. 11.5 In a study of automobile collision insurance costs, a random sample of n = 35 repair costs of front-end damage caused by hitting a wall at a specified speed had a mean of $1,438. Given that o = $269 for such data, what can be said with 98% confidence about the maximum error if y = $1.438 is used as an estimate of the average cost of such repairs? Also, construct a 90% confidence interval for the average cost of such repairs. 11.8 Before bidding on a contract, a contractor wants to be 95% confident that he is in error by no more than 6 minutes when using the mean of a random sample to estimate the average time it takes for a certain kind of adobe brick to harden. How large a sample will he need if he can assume that o = 22 minutes for the time it takes for such brick to harden? 11.9 It is desired to estimate the average number of hours of continuous use until a model 737 airplane will first require repairs. If it can be assumed that o = 138 hours for such data, how large a sample is needed to be able to assert with a probability of 0.99 that the sample mean will be off by no more than 40 hours