developed a new surgical procedure He wants to estimate the difference between the mean recovery time of patients who have the new procedure and the mean recovery time of patients who have the standard procedure The doctor studies a random sample of 11 patients who have the new procedure and a random sample of 9 patients who have the standard procedure These samples are chosen independently The doctor records each patient s recovery time in days The patients who had the new procedure have a sample mean recovery time of 320 2 with a sample variance of 1968 8 The patients who had the standard procedure have a sample mean recovery time of 350 1 with a sample variance of 422 1 Assume that the two populations of recovery times are approximately normally distributed Let be the population mean recovery time of patients who have the new procedure Let be the population mean recovery time of patients who have the standard procedure Construct a 99 confidence interval for the difference Then find the lower and upper limit of the 99 confidence interval Carry your intermediate computations to three or more decimal places Round your answers to two or more decimal places If necessary consult a list of formulas Lower limit Upper limit X