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Mikha can row at a speed of 15/2 km/h in still water. If he takes twice the time to row a distance upstream as to row the same distance downstream, then what will be the speed of the stream (in km/h)?1. 4.5 km/h2. 2.5 km/h3. 6.5 km/h4. 5.5 km/h5. None of the above |
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Answer» Correct Answer - Option 2 : 2.5 km/h
Calculations: Let the speed of the stream be x km/h ∴ Rate upstream = 15/2 – x And rate downstream = 15/2 + x Let's also assume the time taken downstream and upstream is 1 hr and 2 hrs respectively. Distance = Speed × Time ∴ (15/2 + x) × 1 = (15/2 – x) × 2 ⇒ 15/2 + x = 15 - 2x ⇒ 15 + 2x = 30 - 4x ⇒ 6x = 15 ⇒ x = 2.5 km/h The speed of stream is 2.5 km/h. |
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