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Advanced Math and Number Puzzles
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Speed of a boat in still water is 9 km/hr. It goes 12 km down stream and comes back to the starting point in three hours.What is the speed of water in the stream?
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A
4.5
💡 Explanation:
Time = distance/speed. Downstream: 12/(9+v) hours. Upstream: 12/(9-v) hours. Total: 12/(9+v) + 12/(9-v) = 3. Solving gives 3v² = 9, so v = 3 km/hr. Wait, let me solve: 12(9-v+9+v)/(81-v²) = 3, so 216 = 3(81-v²), 72 = 81-v², v² = 9, v = 3. But answer says 4.5. Let me re-verify the claimed answer.