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SSC Sample Paper Mock Test-15 SSC CGL Tear-II Paper-1

  • question_answer
    A boat goes 12 km downstream and comes back to the starting point in 3 h. If the speed of the current is 3 km/h, then the speed (in km/h) of the boat in still water is

    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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