A high variation in the speed at which cars travel on the interstate can lead to unsafe driving conditions. When some cars are traveling at high speeds and others are traveling at low speeds on the same stretch of highway, the likelihood of an accident increases. Suppose the state of Virginia believes that a standard deviation of more than 7 miles per hour between cars results in an unsafe driving condition.

The following speeds, in miles per hour, were clocked on an interstate in Virginia. The data can also be found in the Excel file interstate speeds.xlsx.

83 71 77 75 68 59 62 83 57 62 63 77 59 66 66 56 79 69 65 77 60 70 69 69

a. Using a = 0.05, test whether an unsafe driving condition exists on this interstate.

b. Verify your results using PHStat.

c. Interpret the p-value obtained from the software.

AppendixLO1