| A boat takes 9 h to travel a distance upstream and takes 3 h to travel the same distance downstream. If the speed of the boat in still water is 4 km/h, then what is the velocity of the stream? [SSC (CPO) 2013] |
A) 4 km/h
B) 3 km/h
C) 6 km/h
D) 2 km/h
Correct Answer: D
Solution :
| Let velocity of the stream be \[x\,\,km/h.\] |
| \[\therefore \]Velocity of the boat downstream \[=(4+x)\,\,km/h\] |
| and velocity of the boat upstream \[=(4-x)\,\,km/h\] |
| According to the question, |
| \[3\,\,(4+x)=9\,\,(4-x)\] |
| \[\Rightarrow \] \[12+3x=36-9x\]\[\Rightarrow \]\[12x=24\] |
| \[\therefore \] \[x=2\,\,km/h\] |
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