On a test in a statistics class the mean mark was 69.71 and the standard deviation was 11.65. However, only twenty-one of the twenty-two students now enrolled took the test, as one student was unable to take it because of ill health.

a. Assume this one student has been attending class as much as the other twentyone students until the time of the test. Find the 95 percent confidence interval for the mean mark that would have been obtained in the first test had all twentytwo students been able to take it.

b. The absent student's health deteriorates further and she withdraws from the class. What now is the 95 percent confidence interval for the mean mark of the class? P-963