Aptitude - Problems on Trains - Discussion

What we know is:

t1 length=270m.
t1 speed = 120km/h or 33.33m/s.
t2 length = x,
t2 speed = 80km/h or 22.22m/s.
total speed = 9 seconds.

We need to find the relative speed, so its done like this because the trains are moving towards each other.

33.33m/s+22.22m/s = 55.55m/s.

Now we have all the information we need to solve the length of train 2.

270m+Xm
-------------- = 9s.
55.55m/s

Now we find the total length of both trains combined. We use the information we have. 55.55m/s is now converted to its opposite function, from division to multiplication. 55.55m/s * 9s = 499.95m.

So 499.95m is the total length of both trains combined, so now we can solve train 2's length by completing this final equation.

x= 499.95m-270m = 229.95m. round up to 230m, therefore train 2's length is 230m.

On cross multiplication we get,

9 (500) =4500.
Then, 9 (270+x), 9 goes to another side.
270+x=4500/9,
270+x=500,
X=500-270.

Finally, we get 230.

If we want to find kmph means 15/8.
mph means 8/15 simple formula.

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.

Relative speed is to be found when two moving objects or trains are given.

Please, tell me when to find relative speed?

Distance =speed *time,
D=120+80km/h*9,
D=200*5/18*9,
D=1000/2,
D=500-270=230m.

Trains running in opp directions.

Relative speed 120+80 =200.
By converting into m/s,
200*5÷18 =500/,
We know by formula
L=s*t.
Let x be the length of another train
Therefore
X+270=500÷9*9.
X=500-270= 230.
So, x=230m.

Relative speed is 120 +80 =200.
Now l =s*t =200*5/18*9=500,
Now, the total dist minus 500-270=230m.

Another train's speed and time is already given from that we can calculate the trains length easily why we go for oppostie train?