Almost all smart devices (phones, tablets, and computers) are made with touch screens. A concern of many consumers is the shelf life of the touch component of the screens. A consumer advocacy group wanted to inform its members of a range that they can expect their touch screens to last. The group took a sample of 29 screens and measured the life of the touch function of the screens. That is, they used digital devices to simulate billions of touches to determine the life of the screens. Of the 29 screens sampled, the average touch life was 75 months with a standard deviation of nine months. Construct a 90% confidence interval for the standard deviation of the life of the touch screens. Assume that the life of the touch screens has an approximately normal distribution. Round any intermediate calculations to no less than six decimal places and round the endpoints of the interval to four decimal places.

lower endpoint =

upper endpoint =