For this.. mainly 2 factors really matter.

1. speed of both train
2. length of the both train..

now... let length of two train be x nd y... nd speed if both train id m nd n... then,

total distance = (x+y) unit
total speed = (m+n) unit / hrs

nd then tym taken by train to pass out = [ (x+y)/(m+n) ] hrs

hope u got it !!

Introduction:
When two trains are running in opposite directions, they will eventually meet or cross each other at some point. To find the time when they cross each other, we need to consider their speeds and the distance between them.

Step 1: Identify the given information:
- Speed of the first train (let's call it Train A)
- Speed of the second train (let's call it Train B)
- Distance between the two trains

Step 2: Determine the approach:
To find the time when the two trains cross each other, we can use the concept of relative speed. The relative speed of two objects moving in opposite directions is the sum of their individual speeds.

Step 3: Calculate relative speed:
To calculate the relative speed of Train A and Train B, we add their individual speeds. The formula for relative speed is:
Relative Speed = Speed of Train A + Speed of Train B

Step 4: Calculate the time taken:
The time taken for the two trains to cross each other is equal to the distance between them divided by the relative speed. The formula for time is:
Time = Distance / Relative Speed

Step 5: Plug in the values and solve:
Now, you can substitute the given values into the formulas and solve for the time taken.

Example:
Let's consider an example to understand the process better. Suppose Train A is traveling at a speed of 60 km/h and Train B is traveling at a speed of 80 km/h. The distance between them is 500 km.

Relative Speed = 60 km/h + 80 km/h = 140 km/h
Time = 500 km / 140 km/h ≈ 3.57 hours

Therefore, the two trains will cross each other approximately 3.57 hours after they start moving towards each other.

Conclusion:
To find the time when two trains running in opposite directions cross each other, we need to calculate the relative speed by adding their individual speeds. Then, we divide the distance between them by the relative speed to find the time taken. By solving the equations, we can determine the exact time when the two trains will meet.