a major department store chain is interested in estimating the average amount its credit card customers spent on their first visit to the chain’s new store in the mall. fifteen credit card accounts were randomly sampled and yzed with the sample mean 50.5 dollars and sample variance 400. construct a 95% confidence interval for the average amount its credit card customers spent on their first visit to the chain’s new store in the mall, assuming that the amount spent follows a normal distribution.
in testing for differences between the means of two related populations, the null hypothesis is
a large national bank charges local companies for using their services. a bank official reported the results of a regression ysis designed to predict the bank’s charges (y) -- measured in dollars per month -- for services rendered to local companies. one independent variable used to predict service charge to a company is the company’s sales revenue (x) -- measured in millions of dollars. data for 21 companies who use the bank’s services were used to fit the model: the results of the simple linear regression are provided below. a 95% confidence interval for is (15, 30). interpret the interval.