Question: To help make a decision about expansion plans, the president of a music company needs to know how many compact discs teenagers buy annually. Accordingly, he commissions a survey of 250 teenagers. Each is asked to report how many CDs he or she purchased in the previous 12 months. Estimate with 90% confidence the mean annual number of CDs purchased by all teenagers. Assume that the population standard deviation is three CDs. Survey data are in file Xr10-39.