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?

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Question: 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?
[A].

10

[B].

12

[C].

15

[D].

20

Answer: Option B

Explanation:

Speed of the first train = 120 m/sec = 12 m/sec.
10
Speed of the second train = 120 m/sec = 8 m/sec.
15

Relative speed = (12 + 8) = 20 m/sec.

Required time = (120 + 120) sec = 12 sec.
20