The current of a streams runs at 1 kmph . A motor boat goes 35 km upstream and back again to the starting point in 12 hours. The speed of the motor boat in the still water is?

 

  • Option 1)

     

    6 kmph

     

  • Option 2)

     

    7 kmph

     

  • Option 3)

     

    9 kmph

     

  • Option 4)

     

    5 kmph

     

  • Option 5)

     

    8 kmph

     

Answers (1)

Let's assume the speed of motorboat is x.

Stream Speed = 1

Upstream Speed = x-1

Downstream Speed = x+1

According to question,

\frac{35}{x+1}+\frac{35}{x-1} = 12

\frac{35x - 35 + 35x + 35}{x^{^2}-1}= 12

70x = 12x^{2}-12

12x^{2}-70x-12 = 0

x=6, -1/6

Answer is 6.

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