The Journal of Environmental Engineering (Feb. 1986) reported on a heat transfer model designed to predict winter heat loss in wastewater treatment clarifiers. The analysis involved a comparison of clear-sky solar irradiation for horizontal surfaces at different sites in the Midwest. The day-long solar irradiation levels (in BTU/sq. ft.) at two midwestern locations of different latitudes (St. Joseph, Missouri, and Iowa Great Lakes) were recorded on each of seven clear-sky winter days. The data are given in the table. Find a 95% confidence interval for the mean difference between the day-long clear-sky solar irradiation levels at the two sites. Interpret the results.    

Transcribed Image Text:

SOLARAD Date St. Joseph, Mo. lowa Great Lakes December 21 782 593 January 6 965 672 January 21 948 750 February 6 1,181 988 February 21 1,414 1,226 March 7 1,633 1,462 March 21 1,852 1,698