Aptitude - Problems on Trains - Discussion

Distance=speed*time.
1st train time =27sec. 2nd train time =17sec.
two trains can cross the each other in opposite direction is 23 sec.
so total time=(total distance)/totalspeed;
total distance,
1st&2nd train have speed x,y;
total distance=27x+17y; total speed=x+y;
23=(27x+17y)/x+y;
23x+23y=27x+17y;
6y=4x;
6/4=x/y;
3/2=x/y;
3:2

27x+17y total distance.

X+y=total speed.

Total distance/total speed=total time.

Total time= 23 given.

Solve it.

Can anyone tell me the formulas for relative speed ?

I agreee with Rohit calculation.

Fast calculation = mod(23-17) : mod(23-27) = 6:4 = 3:2 .

@k.kiran kumar
27x+17y/x+y
here as the two trains cross each other total distance they travelled is length of them.As given in problem they cross in 23 seconds.
time=distance/speed
i.e 23=27x+17y/x+y

X+Y is speeds of 2trains and 27x+17y is length of trains
so lenth/speed=time

Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. The ratio of their speeds is:.

Its given as Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds.

So it should be taken as 27x and 17x seconds only, I don't know why it is given as 27x and 17y meters and also denoted as length of train. Please any one explain me?

As we know that,when two train of length l1 and l2 travels in opposite direction with speed let s1 km/hr and s2 km/hr respectively then time taken to cross each other is given by formula

t=(l1+l2)/(s1+s2)

So by using this formula we can easily solve the above problem.

here l1=27*s1=27s1.
l2=17*s2=17s2.

and t is given in problem equal to 23.

therefore,
23=(27s1+17s2)/(s1+s2)=>3:2

I didn't understood why x+y is divided by the term 27x+17y... can any body help to explain clearly