Multiple choice

A boat takes 6 hours to travel certain distance against the stream and comes back to the starting point. If the speed of boat in still water is 4 km/hr. What is the distance between the two points? एक नाव धारा के विरूद्ध एक निश्चित दूरी जाकर प्रारंभिक बिन्दु तक आने में 6 घण्टे लेता है। यदि नाव की चाल शांत जल में 4 किमी./घण्टा है। दोनों बिन्दु के बीच की दूरी क्या है?

  1. 10 km. 10 किमी.

  2. 8 km. 8 किमी.

  3. 7 km. 7 किमी.

  4. 6 km. 6 किमी.

  5. Cannot be determined निर्धारित नहीं किया जा सकता है।
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E Correct answer
Explanation

Let stream speed be s km/hr. Distance = d. Total time = d/(4-s) + d/(4+s) = 6. Solving gives d = 12(4-s^2) km. Since s is unknown but must be less than 4 (otherwise boat cannot go upstream), there are multiple possible (s,d) pairs. Without additional information about the stream, distance cannot be uniquely determined.

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