The head of public safety notices that the average driving speed at a particular intersection averages = 35 mph with a standard deviation of = 7.5 mph. After a school speed limit sign of 20 mph is placed at the intersection, the first 40 cars travel past at an average speed of 32 mph. Using the .01 significance level, was there a significant change in driving speed?

Can you help with part b & c

b. Sketch the distributions involved.

c. Figure the confidence limits for the 99% confidence interval.