A) 5 h 50 min
B) 6 h
C) 6 h 50 min
D) 12 h 10 min
Correct Answer: C
Solution :
Let the speed of motorboat be 36x km /h and that of the current of water be 5x km/h. Speed downstream\[=\left( 36x+5 \right)\,km\text{/}h=41x\text{ }km\text{/}h\] Speed upstream \[=(36-5x)\,\,km/h=31x\,\,km/h\] Time taken to cover the same Distance covered downstream\[=\left( 41x\times \frac{31}{6} \right)\,\,km\] Distance upstream\[=\left[ \frac{(41\times 31)x}{6}\times \frac{1}{31x} \right]h\] \[=\frac{41}{6}\,\,h=6\,\,h\,\,50\,\,\min \]
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