A) 25 km/h
B) 22 km/h
C) 15 km/h
D) 19 km/h
Correct Answer: B
Solution :
Let the speed of the boat in still water be x km/h. \[\therefore \]Speed of the boat in the direction of current \[=(x+2)=\text{km/h}\] and speed of the boat against the current \[=(x-2)\text{km/h}\] \[\therefore \]According to the question, \[\frac{20}{x+2}+\frac{20}{x-2}=\frac{110}{60}\] \[\frac{20\,\,(x-2+x+2)}{(x+2)(x-2)}=\frac{11}{6}\] \[\frac{40x}{{{x}^{2}}-4}=\frac{11}{6}\] \[11{{x}^{2}}-44=240x\] \[11{{x}^{2}}-240x-44=0\] \[(x-22)(11x+z)=0\] \[x-22=0\Rightarrow x=22\,\,\text{km/h}\]
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