Aptitude - Problems on Trains - Discussion

Right. But in the question trains are running in opposite side.

So speed is subtracted ie 120-80 = 40.

Am I correct?

Why we writing denominator 9 for x+270?

how we take x+270÷9? Please explain.

The first train is 270 meters long.
It runs at a speed of 120 km/h.
The second train runs in the opposite direction at 80 km/h.
Both trains cross each other in 9 seconds.
We need to find the length of the second train.
Now we need convert speeds into meters per second:

First train speed:
120*18/5 = (120*5)/18 = 600/18 = 33.33m/s.

Second train speed:
80*5/18 = (80*5)/18 = 400/18 = 22.22m/s.

Now, Find the total speed when the two trains run opposite.
When two trains run opposite each other, their speeds add up.
Total speed = 33.33+22.22,
= 55.55m/s.

Total distance= Total speed×Time.
= 55.55×9.
= 500meters.

Now,Find the length of the second train
Length of first train+Length of second train = 500
We know the first train length = 270 meters,
So,270+Length of second train = 500

Length of second train = 500 − 270 = 230.

Thanks everyone, for explaining it.

What will happen if both trains are in the same direction as we relative velocity we can subtract but how the equation will come?

Please tell me.

D = S*T = 270+x = 500/9*9.

So x = 500-270 = 230.

Thanks alot. It is very helpful to me.

When we add the relative speed when substract please tell me?

It's simple and just take it easy.

When two trains running on the same site then relative speed is add, running in opposite site then we subtract it.