Multiple choice

The speed of a boat along the stream is 12 kmph and it travels a distance along the stream in 91.5 hours. The speed of the boat against the stream is 8 kmph. What is the time taken by the boat to cover the same distance in still water. धारा के अनुकूल एक नाव की चाल 12 किमी./घंटा है और धारा के अनुकूल यह किसी निश्चित दूरी को 91.5 घंटे में तय करती है | धारा के प्रवाह के प्रतिकूल धारा की चाल 8 किमी./घंटा है समान दूरी को स्थिर जल में नाव द्वारा लिया गया समय क्या है ?

  1. 108.9 hours/घंटे

  2. 108.8 hours/घंटे

  3. 19.8 hours/घंटे

  4. 109.8 hours/घंटे
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D Correct answer
Explanation

Downstream speed = 12 kmph, upstream = 8 kmph. Distance = 12 × 91.5 = 1098 km. In still water, speed = (12+8)/2 = 10 kmph. Time in still water = 1098/10 = 109.8 hours. Still water speed is the average of downstream and upstream speeds.

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