Problems on Trains Shortcuts Tips and Tricks(Question 2) | Bank PO Aptitude Exam

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A train running at 45 km/hr takes 36 sec to pass a platform.
The same train takes 12 sec to pass a man walking at the speed of .
15km/h in the same direction. Find the length of the platform.
We should first draw a quick diagram to understand the situation.
Suppose this is the platform of length x.
Let this be the train that has just touched the platform.
The length of the train be L.
The train will have crossed the platform if it covers this distance equal to L + x.
We have been given that this distance is covered in 36 seconds at a speed of 45km/h.
We can write this by the speed and distance formula.
Put the values and convert the km/h to m/s.
We can simplify it to get the total as 450.
Next, take the case of man.
Suppose this is the train.
Let this be the man moving at 15 km/h here.
He has just now been touched by the train.
The man is also moving towards the right.
The train will able to cover the distance L at a net speed of 45 - 15 = 30 only.
So the train will completely pass the man if it covers L meters at 30 km/h.
Again we can use the speed distance formula.
Put the values of 30 and 12 and convert to m/s.
We get L = 100 meters.
Put this L here.
We get x equal to 350 meters.