Two trains 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:

Step 1: Understand what's given

• Train A length = 140 meters
• Train B length = 160 meters
• Speed of Train A = 60 km/h
• Speed of Train B = 40 km/h
• They are moving in opposite directions on parallel tracks.

Step 2: Use relative speed

Since they are moving in opposite directions, we add their speeds:

Relative speed = 60 + 40 = 100 km/h
Convert km/h to m/s: 100 × (1000 / 3600) = 100 × 5/18 = 27.78 m/s

Step 3: Total distance to be covered

They will completely cross each other when they cover the sum of their lengths:

Total distance = 140 + 160 = 300 meters

Step 4: Calculate time

Time = Distance / Speed = 300 / 27.78 ≈ 10.8 seconds

Answer: Approximately 10.8 seconds

Therefore, the two trains will take about 10.8 seconds to completely cross each other.

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This is a typical question on trains involving relative speed. Always remember to:

• Convert km/h to m/s when using meters.
• Add speeds when objects move in opposite directions.
• Use total length when two objects need to fully cross each other.

Such questions are important in aptitude tests and competitive exams.