Multiple choice

The speed of a boat in still water is 7 km/hr and the speed of the current is 1.4 km/hr. A boatman rows everyday to a temple which is 67.2 km away and comes back to the starting point. The total time taken for this two-way journey is

  1. 20 hours

  2. 21 hours

  3. 22 hours

  4. 23 hours

  5. 30 hours
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A Correct answer
Explanation

Speed downstream = 7 + 1.4 = 8.4. Speed upstream = 7 - 1.4 = 5.6. Time = 67.2/8.4 + 67.2/5.6 = 8 + 12 = 20 hours.

AI explanation

The downstream speed is the sum of the boat's speed and the current's speed, which is 7 plus 1.4, equaling 8.4 km/hr. The upstream speed is the difference, which is 7 minus 1.4, equaling 5.6 km/hr. The time taken to travel to the temple is 67.2 divided by 8.4, which equals 8 hours, and the return time is 67.2 divided by 5.6, which equals 12 hours. The total time for the two-way journey is 8 plus 12, resulting in 20 hours.

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