Multiple choice

With an average speed of $40$ km/hr a train reaches its destination in time. If it goes with an average speed of $35$ km/hr it is late by $15$ minutes. The total journey is

  1. $75$ km
  2. $70$ km
  3. $80$ km
  4. $60$ km
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let distance be D. Time 1 = D/40, Time 2 = D/35. Difference = D/35 - D/40 = 15/60 = 1/4 hours. (8D - 7D) / 280 = 1/4. D/280 = 1/4. D = 70 km.

AI explanation

Let the exact time to reach the destination be t hours; using the constant distance equation, 40t equals 35(t + 15/60). Solving this equation gives t equal to 3.5 hours. Using the Time, Speed and Distance formula, the total distance is 40 km/hr multiplied by 3.5 hours, which is 70 km.

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