Question: The SEC requires companies to file annual reports concerning their financial status. It is impossible to audit every account receivable. Suppose an auditor audits a random sample of 49 accounts receivable invoices and finds a sample average of $128 and a sample standard deviation of $53.
a. Find a 99% confidence interval for the mean size of an accounts receivable invoice. Does your answer require the sizes of the accounts receivable invoices to be normally distributed?
b. How large a sample is required for you to be 99% sure that the estimate of the mean invoice size is accurate within $5?