Two trains run in the same direction on parallel tracks at 45 km/h and 36 km/h. A passenger sitting in the slower train notices that the faster train takes 30 seconds to pass him completely. How long is the faster train?

Explanation

1. 01

   The passenger moves with the slower train, so the relative speed is $45 - 36 = 9$ km/$h = 2.5$ m/s.

2. 02

   The faster train passes a point (the passenger), so it covers only its own length.

3. 03

   Length $= 2.5 \times 30 = 75$ m.