Aptitude - Problems on Trains - Discussion

Can anyone please tel me how x+y is came.

They asked to find speed of that we have to use speed = length\time only know but how x+y is came.

This is very good method to understand.

This method is easiest method I can understand this sum.

@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.

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!

Hi I have one doubt.

How X and Y seconds become metres?

Total Distance/Total Speed = Total Time;

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

#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)

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 ?