Police recorded the average speed of cars driving on a busy street by a school. for a sample of 2525 speeds, it was determined that the average amount over the speed limit for the 2525 speeds was 10.110.1 mph with a standard deviation of 77 mph. the 9595% confidence interval estimate for this sample is 7.217.21 mph to 12.9912.99 mph. a) what is the margin of error for this problem? b) what size sample is needed to reduce the margin of error to no more than plus or minus±11?