Problems on trains

Quantitative Aptitude (CSC)

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Train A travelling at 126 km/hour speed, completely crosses Train B in 9 seconds. Train B is half the length of Train A and is travelling at a speed of 90 km/hour in the opposite direction (towards Train A). How much will Train A take to cross a platform of length 690 metres?

28 seconds

32 seconds

25 seconds

30 seconds

Explanation:

Let the length of train A be x meter.
∴ Length of train B = x/2 meter
Speed of train A = 126 kmph
= (126 × 5/18) m/sec = 35 m/sec.
Speed of train B = 90 kmph
= (90 × 5/18) m/sec. = 25 m/sec.
= length of trains A and B/ Time taken in crossing
= 35 + 25 = [x(x/2)/9] = 60 × 9 = 3x/2
= 3x = 90 × 12
= x = (90 × 120/3) = 360 meter
∴ Time taken in crossing the platform
= Length of train A and Platform/(Speed of train A)
= (360 + 690)/35
= 1050/35 seconds
= 30 seconds

By: Pranav Gupta

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