Explain the probability that the average length of a sheet is between 30.25 and 30.35 inches long.
The population of lengths of aluminium-coated steel sheets is normally distributed with a mean of 30.05 inches and a standard deviation of 0.2 inches. A example of four metal sheets is randomly selected from a batch. Explain what is the probability that the average length of a sheet is between 30.25 and 30.35 inches long?