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SSC Sample Paper SSC CGL - Sample Paper-16

  • question_answer
    The speed of the current is 5 km/h. A motorboat goes 10 km upstream and back again to the starting point in 50 min. The speed, in km/h, of the motorboat in still water is

    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 \[x\ne -1\]        


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