Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?

Difficulty: Easy

10 s
12 s
14 s
16 s

Correct Answer: 12 s

Explanation:

Given Data

Equal train lengths = 120 m each
Times to pass a post: 10 s and 15 s

Step 1: Find individual speeds
v₁ = 120/10 = 12 m/sv₂ = 120/15 = 8 m/s

Step 2: Cross each other in opposite directions
Relative speed = 12 + 8 = 20 m/sDistance = 120 + 120 = 240 mt = 240 ÷ 20 = 12 s

Final Answer
They will cross in 12 s.

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