Multiple choice

A train starts from X and proceeds towards Y, which is at a distance of 55 km, at a speed of 40 km/hr. After covering a certain distance, it increases its speed to 50 km/hr and reaches Y in 1 hour 15 minutes after leaving X. After how long does the train change its speed?

  1. 30 minutes

  2. 38 minutes

  3. 45 minutes

  4. 52 minutes

  5. 60 minutes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let d be the distance covered at 40 km/hr in time t. The remaining distance (55-d) is covered at 50 km/hr. Total time is 1.25 hours. So, t + (55-40t)/50 = 1.25. Multiplying by 50: 50t + 55 - 40t = 62.5, which gives 10t = 7.5, so t = 0.75 hours or 45 minutes.

AI explanation

The total travel time is 1 hour 15 minutes, which equals 1.25 hours. Let the distance traveled at 40 km/hr be d kilometers; the equation becomes d divided by 40 plus (55 minus d) divided by 50 equals 1.25. Multiplying the entire equation by 200 gives 5d plus 220 minus 4d equals 250, resulting in d equals 30 km. The time taken to cover this initial distance is 30 divided by 40 hours, which equals 0.75 hours, or 45 minutes.

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