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Saransh can row a boat 10km upstream and 12 km downstream in same time. The ratio of speed of boat in still water to the speed of stream?
1. 1 ∶ 10
2. 11 ∶ 1
3. 22 ∶ 1
4. 12 ∶ 5
5. 17 ∶ 4

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Correct Answer - Option 2 : 11 ∶ 1

Formula used

speed of boat in still water be u and the speed of stream be v

Speed upstream = (u - v) km / hr

Speed downstream = (u + v) km / hr

Calculations     

Time taken to row upstream = \(\frac{{10}}{{{\rm{u}} - {\rm{v}}}}\) hr         ---(1)

Time taken to row downstream = \(\frac{{12}}{{{\rm{u}} - {\rm{v}}}}\) hr         ---(2)

On equating (1) and (2) and solving, we get

⇒ u ∶ v = 11 ∶ 1

Hence The ratio of speed of boat in still water to the speed of stream is 11 ∶ 1

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