patients To do so you select a random sample of 32 heart valve surgery patients and you record the surgery duration for each Assume it is known that the population standard deviation of the durations of all heart valve surgeries is 1 92 hours Based on your sample follow the steps below to construct a 99 confidence interval for the population mean of the surgery durations for all heart valve patients If necessary consult a list of formulas a Click on Take Sample to see the results from your random sample of 32 heart valve patients Take Sample Sample size 0 Point estimate Population standard deviation Critical value 0 Compute 0 00 0 00 Number of patients 32 Enter the values of the sample size the point estimate for the population mean the population standard deviation and the critical value you need for your 99 confidence interval Choose the correct critical value from the table of critical values provided When you are done select Compute 2 00 Sample mean 4 81 Standard error 4 00 Margin of error Sample standard 99 confidence interval 99 confidence interval deviation 1 21 6 00 X Confidence level 99 b Based on your sample enter the lower and upper limits to graph the 99 confidence interval for the population mean of the surgery durations for all heart valve patients 95 90 Population standard deviation 1 92 8 00 Critical value 20 005 2 576 20 025 1 960 20 050 1 645 10 00 10 00