A) 8 km/h
B) 6 km/h
C) 9 km/h
D) 10 km/h
Correct Answer: A
Solution :
Let speed upstream be x km/h and the speed' downstream be y km/h. |
Then, \[\frac{30}{x}+\frac{44}{y}=10\] ?(i) |
and \[\frac{40}{x}+\frac{55}{y}=13\] |
Multiplying Eq. (ii) by 4, Eq. (i) by 5 and subtracting, we get,\[\frac{10}{x}=2\] \[\Rightarrow \]\[x=5\] |
Putting x = 5 in Eq. (i), we get \[4y=44\] |
\[\Rightarrow \]\[y=11\] |
\[\therefore \]Speed upstream = 5 km/h, speed downstream =11 km/h |
Speed of the current \[=\frac{1}{2}(11-5)\,\text{km/h}=3\,\,\text{km/h}\] |
Speed of man in still water |
\[=\frac{1}{2}(11+5)\,\text{km/h}=8\,\,\text{km/h}\] |
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