Aptitude - Problems on Trains - Discussion

The length of the platform = (speed of train * time taken to pass the platform)/(1 - (time taken to pass the man/time taken to pass the platform))

In this case:
The length of platform = (54 * 36)/(1 - (20 / 36))
= (54*36)/(1-(20/36))
= (1944)/(1-(5/9))
= 1944/(4/9)
= 1944 * (9/4) = 240 meters.

I think we don't need 20 secs a train travelling at 54km/hr took.

36 secs to pass a platform means that it covered a distance equal to. Platform in 36 secs simply convert it and the answer is 540m.

t1 =36s
t2 = 20s
s= 54km/hr
l=??

d1 = s*t
d1 = 54*(5/18) * 36
d1 = 15m/s * 36
d1 = 540m.

d2 = 15*20.
d2 = 300m.3

300m is the distance up to the man standing and the length of the total platform would be greater than this. so,

300 + x = 540m.
x = 240m.

540 is the total distance that includes train length+ and platform length.

Here we need only platform length that's why we need train length or you can get another approach like 36-20=16sec. It's the time of starting of the train and the starting of exist platform 15 meters per sec * 16 sec = 240 meters.

As we know Distance = Speed x Time.

Let's find the length of the train --> to find the distance of a train we have to multiply the speed of the train by the time taken by the train to cross a man or pole. so it comes like 15 x 20 = 300 meters.

So, the length of the train is 300 meters

Now when we multiply the train speed with the time taken to cross the platform..... we get the whole length of the train and also the platform length. LIKE --> 15 x 36 = 540 meters .

Now, this length is the whole length of the platform and the train.

To find the platform length subtract the train length that we found out with the whole length
300 - 540 = 240.

240 is the length of the platform.

@All.

Since the train is moving toward the man you can do 36-20 seconds = 16 seconds.

Thanks, everyone for explaining the answer.

Very helpful. Thanks all for giving an explanation.

The speed of train = 54 x 5/18m/s,
= 15m/s.
Length of train = 15 x 20 = 300 meters ∴( distance = speed x time),
Total length = 15 x 30 = 540 (length of train x platform time taken to reach out),
The final answer is 540 - 300 meters.
= 240 meters.

To find the length of the train why we use a 20-second time instead of 36 seconds? Anyone please explain to me.