A) 12
B) 9
C) 8
D) 6
Correct Answer: B
Solution :
If the speed of boat in still water be x km/h, then |
\[\frac{12}{x+3}+\frac{12}{x-3}=3\] |
\[\Rightarrow \] \[12\left( \frac{x-3+x+3}{(x+3)(x-3)} \right)=3\] |
\[\Rightarrow \] \[4\times 2x={{x}^{2}}-9\] |
\[\Rightarrow \] \[{{x}^{2}}-8x-9=0\] |
\[\Rightarrow \] \[{{x}^{2}}-9x+x-9=0\] |
\[\Rightarrow \] \[x\,\,(x-9)+1(x-9)=0\] |
\[\Rightarrow \] \[(x-9)(x+1)=0\] |
\[\therefore \] \[x=9\] because \[x\ne -\,\,1\] |
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