A) 20
B) 26
C) 25
D) 28
Correct Answer: C
Solution :
Let the speed of motorboat in still water be x km/h. \[\therefore \] \[\frac{10}{x-5}+\frac{10}{x+5}=\frac{50}{60}\] \[\Rightarrow \] \[10\left( \frac{x+5+x-5}{(x+5)(x-5)} \right)=\frac{5}{6}\] \[\Rightarrow \] \[20x\times 6=({{x}^{2}}-25)\times 5\] \[\Rightarrow \] \[{{x}^{2}}-24x-25=0\] \[\Rightarrow \] \[{{x}^{2}}-25+x-25=0\] \[\Rightarrow \] \[x(x-25)+1(x-25)=0\] \[\Rightarrow \] \[(x-25)(x+1)=0\] \[\Rightarrow \] \[x=25\] because \[x\ne -1\]You need to login to perform this action.
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