Use the given degree of confidence and sample data to find a confidence interval for the population standard deviation sigmaσ. assume that the population has a normal distribution. round the confidence interval limits to the same number of decimal places as the sample standard deviation. the mean replacement time for a random sample of 20 washing machines is 9.79.7 years and the standard deviation is 2.52.5 years. construct a 99% confidence interval for the standard deviation, sigmaσ, of the replacement times of all washing machines of this type.