Multiple choice

A boat while moving in upstream takes twice the time of going along the stream. If the speed of water is 3 km / h, then find the speed of the boat? एक नाव धारा के विपरीत जाने में धारा के साथ जाने से दोगुना समय लेती है| यदि जल की चाल 3 किमी/घंटा है तो नाव की चाल ज्ञात कीजिये?

  1. 7

  2. 9

  3. 8

  4. 10

  5. 12
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed in still water = b km/h. Speed downstream = b + 3, speed upstream = b - 3. Time upstream = 2 × time downstream. If distance = d, then d/(b-3) = 2 × d/(b+3). Cross-multiplying: d(b+3) = 2d(b-3). Canceling d: b + 3 = 2b - 6. So: 3 + 6 = 2b - b, b = 9 km/h.

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