The Boston public school district has had difficulty maintaining on-time bus service for its students ("A Year Later, School Buses Still Late," Boston Globe, October 5). Suppose the district develops a new bus schedule to help combat chronic lateness on a particularly woeful route. Historically, the bus service on the route has been, on average, 12 minutes late. After the schedule adjustment, the first 36 runs were an average of eight minutes late. As a result, the Boston public school district claimed that the schedule adjustment was an improvement-students were not as late. Assume a population standard deviation for bus arrival time of 12 minutes. The value of the test statistic is ________. A) t₃₅ = -2.00 B) z = -2.00 C) t₃₅ = -0.33 D) z = -0.33

Question

Quizplus · Accepted Answer

Since we are given a population standard deviation, we can use a z-test. The null hypothesis is that the average bus arrival time is still 12 minutes late, while the alternative hypothesis is that the average bus arrival time is less than 12 minutes late (improved). Using the sample mean, sample size, and population standard deviation, we can calculate the test statistic: z = (8-12)/(12/sqrt(36)) = -2.00. Therefore, the correct answer is B.

The Boston Public School District Has Had Difficulty Maintaining On-Time