There's a boy. Let's call him Konrad. He's got his grandparents on father's side east of the city and on mother's side west of the city. Every Sunday, he walks to the train station and takes the first arriving carrier that happens to head towards any of the grandparents' places.
After a while, the mother's parents complain that they hardly see him, while father's parents remark that he's showing up a bit too often. Konrad verifies their story and realizes that he's been visiting the latter almost every weekend, while hardly ever visiting the former.
How is it (statistically) possible?
Some premises to clarify the circumstances for a rigid deduction process.
- It's not a trick question - the answer is statistically deducible.
- There's only one train line and each end point is at one of the grandparents'.
- The train in each direction arrives/leaves exactly every 60 minutes.
- There's never any extraordinary circumstances affecting the schedule.
- The track is single-lane so the trains never arrive at the same time.
- The boy arrives at the station at random occasions.
- The boy has no preferences towards any of the destinations.
- The grandparents are always home.
- There might be multiple trains in service and all travel at a constant speed.
- The boy can board at any non-endpoint station closest to him home.