Aptitude - Problems on Trains - Discussion

Here distance is not mentioned. But you took 27 and 17 as distance. How can we take time interms of distance? Can anyone please explain?

Why we have to take x+y in denominator? Please explain.

Distance is not relative why we add both the lengths?

We should only take either of them.

Let the speed of 1st train be X and 2nd be Y.

So, the distance of 1st train (D= S*T) 27X and 2nd 17Y.
Speed of 2 objects get added if they are in opp direction.
So, speed = X+Y , T= D/S
Then 23= (27X + 17Y)/ X+Y.

The explanation are excellent, but we asked the the speed, so why we calculated the time taken?

If we think let x and y be the length of the trains then, x/27,by/17 will be the speed of the trains respectively and the equation becomes x+y/23b=bx/27+y/17.

Solving we get x/y=81/34.

x+y = total distance.
23 = total time.
Speed = x/27+y/27.
Speed = distance/time.

Therefore x+y/23 = x/27+y/17 is the equation,
Can you tell me why this equation is wrong?

Hello there if anyone did't understood the concept behind it let me explain in my way.
So, everyone know when two bodies are moving towards each other or having an velocity in opposite direction the velocity is add up (e.g you are going on car at 20 m/s and from front the other car is coming at 10 m/s so you will cross each other at 30 m/s) V1+V2.

Now same concept applies here,

S1+S2 = V1T1+V2T2 (S=VT).
S1+S2 / V1+V2 = T1+T2.
AND T1+T2 is 23.
So S1+S2/V1+V2 = 23.

NOW for S1= 27V1 and S2 = 17V2.
Put values in eq and you will get the ratio,
27V1+17V2/V1+V2 = 23.
V1/V2 = 3/2.

Thanks.

s=vt.
t= s/v.
s= distance, v=speed.

27+3 = 30.
17+3 = 20.
30/20 = 3:2.

I can't understand the answer clearly. please explain how we get 3 : 2?