Time, Speed, Distance (RRB)

Core relation: Distance = Speed × Time.

Unit conversion:

• 1 km/h = 5/18 m/s.
• 36 km/h = 10 m/s (memorize).

Average speed (equal distances): 2·v1·v2/(v1+v2). NOT arithmetic mean.

Trains:

• Crossing a stationary object (pole, man): time = train length / speed.
• Crossing platform/bridge: time = (train + platform length) / speed.
• Two trains crossing each other:
  • Same direction: time = (L1+L2)/|v1−v2|.
  • Opposite direction: time = (L1+L2)/(v1+v2).

Boats & Streams:

• Downstream = (b+s); Upstream = (b−s).
• Boat speed = (down+up)/2; Stream = (down−up)/2.

RRB-favorite questions:

1. Train crosses pole/platform — find length/speed.
2. Two trains meeting — find time/distance.
3. Boat upstream/downstream timing.
4. Average speed for round trip.
5. Catching up time (relative speed).