A safety officer is concerned about speeds on a certain section of the New Jersey Turnpike. He records the speeds of 40 cars on a Saturday afternoon. The accompanying table shows a portion of the results; the complete data set, labeled Highway_Speeds, can be found on the text website. Assume that the population standard deviation is 5 mph. Construct the 95% confidence interval for the mean speed of all cars on that section of the turnpike. Are the safety officer’s concerns valid if the speed limit is 55 mph? Explain.
Highway Speeds (mph)
70
65
:
65