Question: Wind Speeds. The average wind speed in Casper, Wyoming has been found to be 12.7 miles per hour, and in Phoenix, Arizona, it is 6.2 miles per hour. To test the relationship between the averages, the average wind speed was calculated for a sample of 31 days for each city. The results are reported below. Is there sufficient evidence at a = 0.05 to conclude that the average wind speed is greater in Casper than in Phoenix?

Casper Phoenix

Sample size 31 31

Sample mean 12.85 mph 7.9 mph

Population standard deviation 3.3 mph 2.8 mph