A manager at a local manufacturing company has been monitoring the output of one of the machines used to manufacture chromium shells. Past data indicate that if the machine is functioning properly, the length of the shells produced by this machine can be modeled as being normally distributed with a mean of 118 centimeters and a standard deviation of 8 centimeters. Suppose 16 shells produced by this machine are randomly selected. What is the probability that the average length of these 16 shells will be between 116 and 120 centimeters when the machine is operating "properly?" Please type your answer in 3 decimal places.