One of the reasons for multiple car accidents on highways is thought to be poor visibility. One of this text’s authors participated in a study of one rural section of highway in Idaho that had been the scene of several multiple-car accidents (source: Michael Kyte, Patrick Shannon, and Fred Kitchener, “Idaho Storm Warning System operational test - final report,”

Report No. IVH9316 (601), National Institute for Advanced Transportation Technology, University of Idaho, December 2000). Two visibility sensors were located near the site for the purposes of recording the number of miles of visibility each time the visibility reading is performed. The two visibility sensors are made by different companies, Scorpion and Vanguard.

Develop a 95% confidence interval estimates of the mean visibility at this location as recorded by each of the visibility sensors. The random sample data are in a file called Visibility. Comment on whether there appears to be a difference between the two sensors in terms of average visibility readings.