The speed of automobiles on I-20 west of FortWorth, Texas, is being investigating by the Texas Department of public Safety (DPs).
If the average speed of cars on the highway exceeds 80 miles per hour (mph), the DPS plans to add more patrol cars to the area. To decide what to do, it takes a random sample of 150 cars and finds the sample average speed to 80.5 mph. Assuming that the population standard deviation is 8 mph, should the DPS add patrol cars to the area?