Aptitude - Problems on Trains - Discussion

In simple process,

Bs-------------------m------------Be

A--------20S---------B------16S---C

l---------------36s---------------l

If man was reference point then T.P=36-20=16s.
We know length=speed*time.
Then lenth of train=(54*5/18)*16=15m/s.*16s.=240m.

Answer=240m.

Why x and 300m are added?

Time taken for reach the platform=36sec.

Time taken for reach a man= 16sec.

Speed (S) = (54*5) /18=15.

Distance between=36-20=16.

Then the distance=16*15.

=240.

Distance=Time*Speed.

* 54 x 5/18 = 15

* 15 x 20(given) = 300

* x+300/36=15
=240m

OR

* Distance = speed*time
* Distance = (54*5/18)*(36-20)
= 15*16
= 240
Speed , Time is given to us. We have to only apply the formula in proper way.

First we are calculate the length of train compared with a man standing on the platform.

= (15*20) m.

=300m.

Second we are calculate the length of train compared with they passes a station platform.

= (15*36) m.

=540m.

We wanted to the length of platform X.

So, the length of platform X and the length of train compared with a man standing on the platform equal to the length of the train compared with they passes a station platform.

X+300m=540m.

X= (540-300) m.

=240m.

We were got the length of platform 240m.

Speed=54*(5/18)=15m/s.

Now time = 36-20=16.

Now distance(i.e length)=speed*time
=15*16
=240m/s.

Friends I think time req. To cross man (20) is less than time req. To cross station (36). So length of station is more than length of train.

So,

Total length of station = 20sec*15m/sec + 16sec*15m/sec.

= lth of train + remaining lth of platform.

For 16 sec,

= 300+240.

= 540m.

I have the same doubt & Its not clear from all these explanations. Why you took 15*20 as the distance value?

Why took 15*20? and the method (36-20) i.e. taking difference can be applicable?

Why can't we take 15*36 to find the length of the train?