The head of public safety notices that the average driving speed at a particular intersection averages 45 mph with a standard deviation of 9 mph. The head of public safety thinks that putting a school speed limit sign of 30mph will decrease the speed at the intersection. After a school speed limit sign of 30 mph is placed at the intersection, the first 35 cars travel past at an average speed of 38 mph. Using the 01 significance level, was there a significant change in driving speed? Use the five steps of hypothesis testing and Calculate and interpret the effect size of the experimental manipulation.
