A college statistics professor has office hours daily. A sample of waiting times to see professor in minutes was taken. The waiting times in minutes were: 10, 12, 20, 15, 17, 10, 30, 28, 35, 28, 19, 27, 25, 22, 33, 37, 14, 21, 20, and 23. Suppose ? = 8.94. Find out the 95% confident interval for population mean.