One hour before the trains meet

Question

Two trains are on the same straight track, heading towards each other. One travels at 60 km/h and the other at 40 km/h. The stations they left are several hundred kilometres apart, and they left at different times.

How far apart are the two trains exactly one hour before they meet?

Accepted Answer

100 km. Closing speed. The trains approach each other at 60 + 40 = 100 km/h. So in the final hour before they meet, the gap between them shrinks by 100 km, from 100 km to zero. One hour before meeting, they are exactly 100 km apart. Why the missing information is a distraction. The distance between the stations and the departure times determine when and where the trains meet, but the question asks about the situation one hour before that moment, whenever it is. Working backwards from the meeting, the only thing that matters is how fast the gap closes. A common overreaction. Some people assume…

One hour before the trains meet

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