# 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

Let's assume the speed of motorboat is x.

Stream Speed = 1

Upstream Speed = x-1

Downstream Speed = x+1

According to question,

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

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

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

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

$x=6, -1/6$