Aptitude - Problems on Trains - Discussion

It should be 65 sec only.

Analysis: The speed of the train is the same in both cases. For the constant speed,

(distance/time) in first case = (distance/time) in second case.

240/24=650/x==> x = 65 sec.

240=24sec.
then 650=x.
240x=650*24,
240x/240=650*24/240,
= 65m/s.

240/24=10,
.:650/10=65+24=89.

Here, the question is asking for a specific time taken by the train to pass the platform (650/10 =65) not the total time is taken. If at all they asked for total time, we would add them up (65+24).

Distance= speed * time,
240/ 24=time,
Time = 10s,
Distance= speed* time.
240+ 650 combing distance = 890,
890/10= time,
89 m/s.

Why did you add 240?

Length of train(distance)=240m
Time=24sec
Formula: length(distance)=speed x time
240=speed x 24
speed=240/24
speed=10sec.

Now it has to pass platform of 650m
The total length of platform =650m
train length = 240m
The total distance the train pass the platform = 650+240=890m.
Because as the train entered the platform(650m) the train remaining part was outside the platform (240m).
So total distance the train cover is 890.

Why we are adding the time of poles with the time of platforms?

Here pole consider as a point of reference, but platform not a point if consider engine only cross the platform from starting of platform to end (i.e also consider as crossed) 65 sec is correct, but if consider entire train (engine to the last van) cross the platform end to end length of the platform should be added hence 89sec is correct.

89 sec is the correct answer.