Multiple choice

If a train crosses a km-stone in 12 seconds, how long will it take to cross 91 km-stones completely if its speed is 60 km/hr?

  1. 1 hr 30 min

  2. 1 hr 30 min 12 sec

  3. 1 hr 51 min

  4. 1 hr 1 min 3 sec
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Crossing 91 km-stones means covering the distance between the 1st and 91st stone, which is 90 intervals of 1 km each. Distance = 90 km. Time = Distance / Speed = 90 / 60 = 1.5 hours. The train also takes 12 seconds to cross the first stone (length of train). Total time = 1 hr 30 min + 12 sec.

AI explanation

Crossing one km-stone means the train travels a distance equal to its own length, which takes 12 seconds. At 60 km/hr, the train travels 91 km between the first and last km-stone, and this 91 km distance takes 91 minutes. To cross the 91st km-stone completely at the end, the train needs an additional 12 seconds. Adding 91 minutes and 12 seconds to the starting time gives a total crossing time of 1 hour 30 minutes 12 seconds.

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