Lena's Package DeliveryDiscrete Mathematics Level 5
A bus line offers trips in both directions between Vancouver, British Columbia and Seattle, Washington. They offer five daily trips in each direction and each trip takes 4 hours. Trips in both directions start at 6:00 am, 9:00 am, 12:00 pm, 3:00 pm and 6:00 pm (from the respective starting points). Lena stays in Vancouver, and needs to take a package to Seattle and drop it off with a friend. Lena's friend can meet her at the bus depot so Lena can leave immediately after dropping off the package, or Lena can stay with her friend for some number of nights. The earliest bus Lena can take is on Sunday at 6:00 am and she needs to get home by the evening of the following Saturday (i.e. the latest bus back those she can take is the 6:00pm bus). How many choices for which two buses to take does Lena have?
Details and assumptions
Lena can leave on Tuesday and come back on Thursday. She clearly cannot leave on Thursday and come back the Tuesday before.
Seattle and Vancouver are in the same time zone.