Question: After an hour of sitting in front of your house, the radar sign has recorded 30 observations of car speeds. The sample mean is 42.1 mph and the speed limit is 40 mph.

A true standard deviation is known to be 5.8 mph. Can we conclude at the 0.05 level of significance that the average driver is speeding?

(a) You have reason to believe that the true standard deviation is incorrect. Instead, you use the sample standard deviation of 5.7 mph. Can we conclude at the 0.10 level of significance that the average driver is speeding?