Aptitude - Problems on Trains - Discussion

Since we are taking relative speed that means the slower train is stationary. And thus the faster train needs to travel only the distance of the slower train. Since both the trains start (assuming) at the same time and with the engines at the same line. The answer comes to be 100 m.

Friends he said it takes 36 sec to cross a train then it means the difference in distance b/n them is x (which is length of train).

So the answer is:

x/(Relative speed) = 36;
x = 100;

Not 50 its wrong.

Fast train 46*(5/18)*36 = 460.

2nd train 36*(5/18)*36 = 360.

Difference = 460-360 = 100.

2 train = 100/2 = 50 (ans).

My question is why we are including ten in the calculation its not given in the data right?

We are finding the relative speed.

Train = ||.

Train 1 = |1| speed is 46 km.

Train 2 = [2] speed is 36 km.

*Diagram:

1. Imagine at (2:00 am) both are moving in parallel direction.

[2] (T1 haven't covered x distance).

|1| at (2:00:36 am).

|1| [2] (T1 covers first x distance).

# At (2:01:13 am).

|1| (T1 covers next x distance).

[2] ((Now t1 coverd 2x distance)).

That's how distance is 2x.

I think the answer should be 100 meters, because in question it is not given the starting positions of trains. So we have to assume they started from same point.

Now let the slower train is at rest then the faster train's speed would be 10 km/hr, and it cross the slower train (length) in 36 sec. So the LENGTH = 10km/hr*30 sec = 100 meters.

Can anyone tell me why only dividing by 36 why not by 46?

The length of the train is equal.

So let it x.

Then applying the formula.

a + b/u - v = Time taken by the faster train passes the lower train.

x + x/46 - 36 = 36.

The speed of trains are in km/hr. So it have to convert in m/sec.

Firstly it subtract.

Because fraction value will come. So it difficult to multiply.

It's either subtract before or after.

Then, 46 - 36 = 10 km/hr.

10 * 5/18 = 25/9.

The answer will come 2x/25/9 = 36.

Then the 9 goes to multiply denominator.

9*2x/25 = 36.

Then for easy calculation 2x/25 = 36/9.

x = 50.

Sir, I am having some difficulties to solve a question. Some confusion is there. I need your help sir. The question is-.

Two trains are running at 40km/hr and 20 km/ hr respectively in the same direction. Fast train completely passes a man sitting in the slower train in 5 sec. What is the length of the fast train?

Sir the formulas is a+b/u-v.

Where a and b lengths and u and v are speeds.

My question is that: why we are not taking both the lengths. In solution, only fast train lengths is taking. Why sir. A/c to formula both the lengths are necessary.