Operating Company


The marketing manager of a branch office of a local telephone operating company wants to study characteristics of residential customers served by her office. In particular, she wants to estimate the mean monthly cost of calls within the local calling region. In order to determine the sample size necessary, she needs an estimate of the standard deviation. On the basis of her past experience, she estimates that the standard deviation is equal to $12. Suppose that a small scale study of 15 residential customers indicates a sample standard deviation of $9.25. At the 0.10 level of significance, is there evidence that the population standard deviation is less than $12?


The local Office of Tourism sells souvenir calendars. Sue, the   head of the office, needs to order these calendars in advance of the main   tourist season. Based on past seasons, Sue has determined the probability of   selling different quantities of the calendars for a particular tourist   season.   Demand for   Calendars Probability of Demand       75,000 0.15   80,000 0.25   85,000 0.30   90,000 0.20   95,000 0.10       The Office   of Tourism sells the calendars for $12.95 each. The calendars cost Sue $5   each. The salvage value is estimated to be $0.50 per unsold calendar.       Determine   how many calendars Sue should order to maximize expected profits    


The test scores on a 100-point test were recorded for   20 students:   71   73   84   77   

a.) Can you reasonably assume that these   test scores have been selected from a normal population? Use a stem and leaf   plot to justify your answer.   

b.) Calculate the mean and standard   deviation of the scores.   

c.) If these students can be considered a   random sample from the population of all students, find a 95% confidence   interval for the average test score in the population.    

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