Speeding. It often appears that most drivers on the road are driving faster than the posted speed limit. Situations differ, of course, but here is one set of data. Researchers studied the behavior of drivers on a rural interstate highway in Maryland where the speed limit was 55 miles per hour.

They measured speed with an electronic device hidden in the pavement and, to eliminate large trucks, considered only vehicles less than 20 feet long. They found that 5690 out of 12,931 vehicles were exceeding the speed limit. Is this good evidence that (at least in this location) fewer than half of all drivers are speeding?

The following exercises concern the optional section on tests for a population mean. To carry out a test, complete the steps illustrated in Example 4 or Example 5.