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Two trains of lengths 100 m and 140 m respectively are running in opposite directions on parallel tracks. If their speed is 29 km/hour and 43 km/hour respectively. In what time will they cross each other?


1. 14seconds 
2. 10 seconds 
3. 20 seconds 
4. 16 seconds 
5. 12 seconds 

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Correct Answer - Option 5 : 12 seconds 

Given:

Length of first train = 100 m

Length of second train = 140 m

Speed of first train = S1 = 29 km/hr

Speed of second train = S2 = 43 km/hr

Formula:

If trains are running in the opposite direction then,

Relative speed = S1 + S2

Crossing time = total length of train/relative speed

Calculations:

Relative speed = (29 + 43) kmph = 72 kmph

⇒ 72 × (5/18)

⇒ 20 m/sec

Required time = total length of train/relative speed

⇒ (100 + 140)/20 = 12

⇒ 12 seconds

Both trains crosses each other after 12 sec.

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