Aptitude - Problems on Trains - Discussion

Hey if we follow the physics concept then relative distance should decrease while crossing each other. Then it should be (27x - 17y)/(x+y). Isn't it?

Why should both trains have different length. Even sometimes they can have same length and can run in different speeds right. Then how can we do like that. Can anyone explain please?

If I divide speed of one train 27 divided by another its almost 1.5 can I choose 3:2. Is it a pure coincidence ?

#Krishna no this is not possible as you say. Then cross each other in 23 sec. Is have no sense?

#Vivek kumar.

Here the questions is : two train of length a and b are run in opposite directions at u m/sec. and v m/sec., then the time taken by the trains to cross each other = (a+b)/(u+v).

And if two train of length a and b are run in same directions at u m/sec. and v m/sec., then the time taken by the faster trains to cross the slower train = (a+b)/(u-v)

Total Distance/Total Speed = Total Time;

27X+17Y/X+Y = 23.

Hi I have one doubt.

How X and Y seconds become metres?

Another way be :

Train A and B meet each other at 23 sec. It is the mean/common time of both the trains. Taking it as the reference train A will take 27-23 = 4 sec to reach end point. Similarly train B will take mod|17-23| = 6 sec to reach other end.

Using Formula:

If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:

(A's speed) : (B's speed) = (under root b : under root a).

A:B = 6:4 =3:2.

Thanks!

@Vadivel.

There may be possible that the lengths are same but in question given that the crossing time is 23. So we will apply the formula of crossing time (a+b)/(u+v). And for length a & b we will use the man crossing conditions.

Please don't apply anything from your side only use the conditions which are given in question.

This method is easiest method I can understand this sum.