| A person can row \[7\frac{1}{2}km\]in \[1\,\,h\] in still water and he finds that it takes him twice as long to row up as to row down the river. The speed of |
A) \[2\,\,km/h\]
B) \[3\,\,km/h\]
C) \[2\frac{1}{2}km/h\]
D) \[3\frac{1}{2}km/h\]
Correct Answer: C
Solution :
| Let speed of stream be \[y\,km/h.\] |
| Rate downstream \[=\left( \frac{15}{2}+y \right)km/h\] |
| and rate upstream \[=\left( \frac{15}{2}-y \right)km/h\] |
| Then, \[2\left( \frac{15}{2}-y \right)=\left( \frac{15}{2}+y \right)\] |
| \[\Rightarrow \] \[15-2y=7.5+y\] |
| \[\Rightarrow \] \[7.5=3y\]\[\Rightarrow \]\[y=2.5km/h\] |
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