What is the length of the fast train?

Question

Two trains are running at 40 km/hr and 20 km/hr respectively in the same direction. Fast train completely passes a man sitting in the slower train in 5 seconds.
What is the length of the fast train?

Answer 1

Relative velocity between the trains is 20 kmph =>
20×5/18 m/s => 50/9 m/s

Now length of the faster train is
(50/9){speed}×(5){time}
Because from the passenger's point of view, the faster train is moving at only the relative velocity and it took 5 seconds for it to pass by him

Therefore the length of the faster train is [27 (7/9)] meters.

Answer 2

Relative speed=s=(40-20)km/hr=(20*5/18)m/sec=50/9m/sec
Length of faster train=d
time=t=5sec
d=t*s
d=5*50/9=250/9=27(7/9)m
Ans :Length of faster train is 27(7/9) meters