Multiple choice

The speed of a boat in still water is 9.5 kmph while that of current is 2.5 kmph. If the boat takes 285 minutes in rowing form point A to B and coming back to point A, what is the distance between point A and B ? एक नाव की स्थिर जल में चाल 9.5 किमी/घंटा है जबकि धारा की 2.5 किमी/घंटा है। यदि नाव बिन्दु A से B तक जाकर वापस बिन्दु A तक लौटने में 285 मिनट लेती है तो बिन्दु A और B की बीच की दूरी क्या है ?

  1. 24 km/किमी

  2. 21 km/किमी

  3. 8.5 km/किमी

  4. 15 km/किमी
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B Correct answer
Explanation

Boat speed in still water = 9.5 kmph, current speed = 2.5 kmph. Downstream speed = 12 kmph, upstream speed = 7 kmph. Total time = 285 minutes = 4.75 hours. If distance is d: d/12 + d/7 = 4.75. Solving: 7d + 12d = 4.75 × 84, so 19d = 399, giving d = 21 km. This tests boats and streams concepts.

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