Question 15
Four one-way tram lines serve the city as shown. Marcus’s home is at A and the theater (Rạp hát) is the lower-right stop. Numbers on segments are travel times in minutes; circles are stops.
- Line A departs A every 3 minutes.
- Line B departs B every 2 minutes.
- Line C departs C every 4 minutes.
- Line D departs D every 5 minutes.
The first departures of all four lines are simultaneous. Stop time is negligible; passengers may change lines at shared stops but may have to wait. What is the shortest time for Marcus to reach the theater?
Editorial start convention: Marcus is ready at A when the first simultaneous departures occur, at time 0; all waiting from that time is counted.
- Line A departs A every 3 minutes.
- Line B departs B every 2 minutes.
- Line C departs C every 4 minutes.
- Line D departs D every 5 minutes.
The first departures of all four lines are simultaneous. Stop time is negligible; passengers may change lines at shared stops but may have to wait. What is the shortest time for Marcus to reach the theater?
Editorial start convention: Marcus is ready at A when the first simultaneous departures occur, at time 0; all waiting from that time is counted.