Problem-8 The manager of a grocery store wants to determine what proportion of people who enter his store are his regular customers. What size sample should he take so that at 95% confidence the margin of error will not be more than 0.1? Problem-9 Six hundred consumers were asked whether they would like to purchase a domestic or a foreign automobile. Their responses are given below. Preference Frequency Domestic 240 Foreign 360 Develop a 95% confidence interval for the proportion of all consumers who prefer to purchase domestic automobiles. Chapter-9 Problems: Problem-10 In the past, the average age of employees of a large corporation has been 40 years. Recently, the company has been hiring older individuals. To determine (hypothesis test) whether there has been an increase in the average age of all the employees, a sample of 25 employees was selected. The average age in the sample was 44 years with a standard deviation of 5 years. Assume population distribution to be normal. Let a = 0.05. a) State the null and the alternative hypotheses. b) Test (hypothesis) to determine whether the mean age of all employees is significantly more than 40 years. Problem-11 A soft drink filling machine, when in perfect adjustment, fills the bottles with 12 ounces of soft drink. A random sample of 25 bottles is selected, and the contents are measured. The sample yielded a mean content of 11.88 ounces, with a standard deviation of 0.24 ounces. With a 0.05 level of significance, test (hypothesis) to see if the machine is in perfect adjustment. 3