Aptitude - Problems on Trains - Discussion

After found the length of the first train then it will come to know about the length of 2nd train because (x/2).

When we find the length of the platform. Why did we use the first train length?

The answer isn't correct. It should be 600m.

Proof: If you go by other way taking length of the platform as 400m and time as 45 seconds.

Then the speed of the train would come as: (400/45)*(18/5)=32kmph(which isn't true)

Can anybody explain this problem clearly ?

@Vineet:

You are wrong buddy,,..you have to add train's length as well.

So it'd be 400+200=600/45*18/5 = 48 kmph.

I think answer for length of the platform is 200m.

(400+y) /45=48*5/18.

Solving this we get y=200m.

According to the problem,

First let us take length of the first train as "x"

So the length of the second train is half of the second train so it is half of x
So the total length is "(3/2)x"

and given that the two trains are travelling in opposite directions so that their relative speed = (48+42)km/hr.
now convert into m/s so it is 90*(5/18) =25 m/s.

from basic rule s = d /t;

25 m/s = ((3/2)x)/ 12 sec
by solving it we get x = 200m

and given that time required to pass platform is 45 sec

and length of platform = z
48 * (5/18) = (200+z) m/ 45 sec

by solving it we get finally 400 m

Could anybody explain clearly. Please. I can't understand. Explain in a simple manner please.

12 sec is used to cross both the train from opposite direction.but 45 sec is used to pass only the platform by the fastest train.

@PRIYA
u r wrong.The length of the train is 200m.
To finding length of the platform,u have to solve this manner.

200+x=48*(5/18)*45

ANS:- 400m.

Please tell me why we have to use 48km ? why not 42 km ?
after finding x=200...?? do answer it.

ie..200+x=48*(5/18)*45