Aptitude - Problems on Trains - Discussion

Now study the problem carefully the given data is
two trains moving in opposite direction . that means we add them 100+100=200mts

to cross these 200mts it takes 8 secs ok
now, they have asked to find the speed of the faster train if the speed is twice the slower train , this is given in the question.

Now ,

speed=distance/time

speed=200mts/8secs ok
as options are given in km/hr , we have to convert speed to km/hr

So we multiply with 18/5
well (200mts/8secs)*18/5=(200/8)*(18/5)=90km/hr
these is the total speed .

Now they asked us to find the speed of the train twice the other train

Let the speed of first train =xkm/hr

Speed of other train should be twice=2x km/hr

So we have got total speed as 90km/hr
x+2x=90km/hr
3x=90km/hr
x=30km/hr
speed of one train is 30km/hr.

So they asked twice the speed of train

So we get 2x=2*30
=60km/hr
Now if we add 30+60=90km/hr

We got the total speed

The speed of the faster train is 60 km/hr

I don't understand please explain it brief.

I didn't understood how can I clear this problem?

Assume one train is moving with X speed than other is twice faster it means 2x

look normal speed =x
twice the above speed=2*x=2x

Hi seema rules wise we have to add the distance, relative speed based on the direction of both trains (same:-, opposite:+).

Here I wanna know! how we suppose to have 2x as fast train. Can any one suggest me"""If one is moving twice as fast the other""". And what about this?

If these two trains are moving in opposite direction then how can we add their distance.

When the train is Opposite direction, than the relative speed is add to both (100+100)= 200

Hi @jelli, I think this is correct.

length of each train=100 m
let speed of one train=x km/h
other is moving twice as fast the other i.e=2*x km/h
speed=distance/time
(x+2x)*5/18=200/8
x=30m
they are asking the speed of faster train which is 2*x
here we land up with x=30

So 2*30=60m

Hi Arun,
Here we are converting km/h to m/s
so 1km=1000 meters
1hr=3600 sec
1km/h=1000/3600 m/s
1000/3600=5/18 m/s