Aptitude - Problems on Trains - Discussion

SIMPLE WAY.

Speed = 54km/hr,
54/3600 * 1000,
=15m/s.

36 sec to pass the platform
15 * 36 = 540.
20 sec to pass the man,
15 * 20 = 300.
i.e distance is 540 - 300 = 240.

There are a platform and train is passing through that platform in 36 seconds and there is a man ON THE PLATFORM, the train passes it in 20 sec. You cannot add both the times because man is standing on the platform. If he were standing outside the platform timings could have been added.

So, Trains speed is 15 m/s and it is a crossing platform in 36 seconds and men is included in it coz he is standing on the platform.
So length of train + length of platform will be = 15 multiply 36 = 540.

Now the length of the platform (you have to subtract the length of the train from total length) = 15 multiply 20 = 300.
So, 540 - 300 = 240.

Length = Speed * Time.
Speed = 54 * 5/18 = 15 m/sec.
Time = 36 - 20 = 16.
Length = 15 * 16.
= 240m.

Easily way.

Train speed is 54 in KM/HR so KM/HR = 1000 M /3600 S = 10/36 = 5/18 * 54 train speed = 15 M/S.

Train crossed in 36 man in 20 so we can minus both so 36 - 20 = 16.
16 * 15 = 240.

Hi, Friends,

Here given is that train takes 36 sec to cover a distance which is the length of the platform. Because here clearly given that. The train which is having speed 54km/hr takes time 36 sec to cover distance i.e the length of the platform. So I think there is no need to take into consideration the length of the train.

Why have we divided by 36?

Hii guys, I think.

Length = speed * time.

We have to find platform length so we have taken the man standing on platform time.

Therefore, length = 15 * 20.

Let me put it straight 300 is the length of the train. Then in the problem, it should be treated as 300 + 300 + length of the platform.

It should take the tip as the entry and tail as exit and by that time it would have covered 600 m.

Friends, this method also can apply.

We know Time is taken by a train to cross a Standing man = (Length of the train) / (Speed of the train).

Thus, 20 = Length of the train/ (54 x 5/18).

So length of the train= 20 x 54 x 5/18 = 300 m.

Also, we know Time taken by a train to cross a Platform.

= (Length of the train+Length of the platform) / (Speed of the train).

I. E, 36= (300 + Length of the platform) / (54 x 5/18).

300+ So length of the platform = 36 x 54 x 5/18 = 540.

So, the length of the platform = 540 - 300 = 240 m.

All of you have got answer rightly. According to my understanding, time spent by a train to cross a man is at the 20s. A man is standing at an extreme end of a train. Thus, a length of the train could be traded.