Question: ACNielsen is a New York-based corporation and a member of the modern marketing research industry. One of the items that ACNielsen tracks is the expenditure on over-the-counter (OTC) cough medicines. ACNielsen recently indicated that consumers spent $620 million on OTC cough medicines in the United States. The article also indicated that nearly 30 million visits for coughs were made to doctors' offices in the United States.
a. Determine the average cost of OTC cough medicines per doctor's office visit based on 30 million purchases.
b. Assuming that the average cost indicated in part a is the true average cost of OTC cough medicines per doctor's visit and the standard deviation is $10, determine the probability that the average cost for a random selection of 30 individuals will result in an average expenditure of more than $25 in OTC cough medicines.
c. Determine the 90th percentile for the average cost of OTC cough medicines for a sample of 36 individuals, all of whom have visited a doctor's office for cough symptoms.