Reading the Bus Schedule
A student in Pohnpei needs to get from her village to the college campus for a 9:00 a.m. class. The bus leaves her village at 7:15 a.m. and arrives at the downtown terminal at 8:05 a.m. From the terminal she can either take a second bus that departs at 8:20 a.m. and reaches campus at 8:45 a.m., or walk, which takes 30 minutes. The second bus runs every 40 minutes, so if she misses the 8:20 bus the next one is at 9:00 a.m. The first bus is sometimes late by up to 15 minutes. She must be on campus by 8:55 a.m. to be on time. She is deciding whether to rely on the connecting bus or plan to walk.
1. Under normal conditions, which option gets her to campus on time, and by how much margin?
Read the worked answer
Under normal conditions the first bus arrives at 8:05. The connecting bus departs 8:20 and arrives 8:45, which is 10 minutes before the 8:55 deadline. Walking from 8:05 takes 30 minutes, arriving at 8:35, which is 20 minutes before the deadline. So both work when everything runs on schedule, and walking actually gives a larger margin (20 minutes vs. 10).
2. The first bus can be up to 15 minutes late. Analyze the risk of each option in that worst case and recommend a plan.
Read the worked answer
If the first bus is 15 minutes late, it arrives at 8:20. The connecting bus departs at exactly 8:20, so she would likely miss it; the next bus is at 9:00 and arrives after the 8:55 deadline, meaning she is late. Walking from an 8:20 arrival takes 30 minutes, arriving at 8:50, which is still 5 minutes before the 8:55 deadline. So in the worst case walking still succeeds while the bus fails. The recommendation is to plan to walk, because walking's outcome is robust to the known 15-minute lateness while the bus connection has zero slack. The reasoning turns on margin versus variability: the bus has a smaller buffer (10 min) than the possible delay (15 min), so it is fragile.