Truck drivers who cannot maintain regular sleep hours due to their work schedule often suffer from insomnia. A recent study on sleeping patterns of truck drivers focused on quantifying deviations from regular sleep hours. A random sample of28professional truck drivers was interviewed, and the drivers in the sample reported the time at which they went to sleep on their most recent working day. The study gave the sample mean and standard deviation of the times reported by drivers, with these times measured in hours after midnight. (Thus, if the driver reported going to sleep at11p.m., the measurement was1.) The sample mean was0.8hours, and the standard deviation was1.8hours. Assume that the sample is drawn from anormally distributed population. Find a90%confidence intervalfor thepopulation standard deviation, that is, the standard deviation of the time (hours after midnight) at which drivers go to sleep on their work days. Carry your intermediate computations to at least three decimal places.

What is the lower limit of the90%confidence interval?

What is the upper limit of the90%confidence interval?