Multiple choice

A man can row two third of whole distance against the stream in same time in which he covered whole distance with the stream. If the speed of the stream is 2 km/hr. Then find the speed of the boat. एक आदमी धारा के विपरीत कुल दूरी के दो - तिहाई भाग को तय करने में उतना ही समय लता है जितना कि धारा के सापेक्ष कुल दूरी को तय करने में लेता है | यदि धारा की चाल 2 किमी /घंटा है | नाव की चाल ज्ञात कीजिये |

  1. 10 km/hr. / किमी /घंटा

  2. 16 km/hr. / किमी /घंटा

  3. 8 km/hr. / किमी /घंटा

  4. 12 km/hr. / किमी /घंटा
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A Correct answer
Explanation

Let boat speed = b, stream speed = 2 km/hr. Downstream speed = b + 2, upstream speed = b - 2. Time for 2/3 distance upstream = time for full distance downstream: (2/3)d/(b-2) = d/(b+2). Cross-multiplying: 2(b+2) = 3(b-2), which gives 2b + 4 = 3b - 6, so b = 10 km/hr. This is a standard boat and stream problem involving time, distance, and relative speeds.

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