State Troopers set up a speed trap on a highway. Because the worst speeders usually have radar detectors, they decide not to use radar. They identify two points that are a known distance apart and position an observer where she can see both points. The observer has a stop watch and a radio. She will identify cars that are speeding and radio the description and tag number of each speeding car to other State Troopers who are waiting just around a bend in the road. The Troopers know that different speedometers have different amounts of error. In order to avoid giving tickets to people who have small speedometer errors and focus on the worst speeders, they decide to allow cars to be a small amount over the speed limit without getting a ticket. A car travelling at the speed limit will take exactly 10 seconds to travel between the two points. The Troopers decide not to give a ticket to anyone who takes 9 seconds or longer to travel between the two points. What is the maximum percent error, to the nearest percent, in the time measurement that the Troopers are allowing in this situation