Multiple choice

A train reaches its destination on time with an average speed of 40 kmph. If it goes with an average speed of 35 kmph, it is late by 15 minutes. Find the length of the total journey.

  1. 70 km

  2. 56 km

  3. 23 km

  4. 78 km

  5. 85 km
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A Correct answer
Explanation

Let distance = d km. At 40 kmph, time = d/40 hours. At 35 kmph, time = d/35 hours. The difference is 15 minutes = 15/60 = 1/4 hours. So d/35 - d/40 = 1/4. d(1/35 - 1/40) = 1/4. d(40 - 35)/(35 × 40) = 1/4. d(5)/(1400) = 1/4. d/280 = 1/4. Therefore d = 280/4 = 70 km.

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