10. The length of useful life of a fluorescent tube used for indoor gardening is normally distributed. The useful life has mean of 600 hours and standard deviation of 40 hr. Determine the probability that a. such a tube will last less than 730 hr. b. Find the 44th percentile. 1 1. The U.S. National Center for Health Statistics reports that 60% of those with artificial hip and knee joints are female; If 30 of these people are selected at random, find the probability that fewer than 15 are female. 12. The Oak Grove College financial aid office did a study showing that their students spend an average (mean) of $680 in the college bookstore on books and supplies per year. The standard deviation is $138. If a random sample of 36 students is surveyed. What is the probability that the mean amount spent for books and supplies is less than $600? 13. A college administrator would like to determine how much time students spend on homework assignments during a typical week. A questionnaire is sent to a sample of n = 100 students and their response indicates a mean of 7.4 hours per week. Let sigma o=3.4 hours. Compute the 95% confidence interval. 14. A company uses automated sprayer to apply paint to metal. The company sets the sprayer to apply the paint one-inch thick. The company wants to estimate the mean thickness the sprayer is applying the paint within 0.0625 inches. Determine the minimum sample size required to construct a 90% confidence interval for the population mean. Assume the population standard deviation is 0.25 inch. 15. The number of years it took a random sample of 32 former smokers to quit permanently is listed. At a = 0.05, is there evidence that it takes them less than 15 years to quit. 26