Aptitude - Problems on Trains - Discussion

Why have we divided by 36?

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.

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.

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

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.

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.

Speed of the train = 54km/hr,
= 54 * 5/18 m/s,
= 15 m/s.

Time = train reach time - man standing time.
= 36 - 20,
= 16s.

Length = Speed * time.
= 15 * 16.
= 240m.

Distance = time * speed.

Sspeed of train = 54 * 5/18 = 15 m/s.
Time taken by train to cross man= 20s,
Therefore distance/length of train = 20 * 15 = 300m,
Time taken to cross platform= 36s.
Length of train + length of platform = time * speed.
Which implies,
Length of platform = (36 * 15) - length of train.
Length of platform = 540 - 300,
Length of platform = 240m.

54 * (5/18) = 15m.
x = 36s y = 20s.
x - y = 16s (dist b/w train reach the station - train reach the man).

Now,
15 * 16 = 240m (speed * dist).
Answer = 240m.

I am unable to understand it. Someone help me.