Question

The current of a stream runs at the rate of 4
km/hr. A boat goes 6 km and back to the
starting point in 2 hours. The speed of the boat
in still water is
a) 10 km/hr
b) 9 km/h
c) 5 kmhr​

Answer 1

Answer:

8km/hr

Step-by-step explanation:

8 km/hr

Let the speed of boat in still water be x km/hr.

\therefore \frac{6}{x+4}+\frac{6}{x-4} = 2

=> 6\left ( \frac{x-4+x+4}{(x+4)(x-4)} \right ) = 2

=> 6x = x^{2}-16

=> x^{2}-6x-16 = 0

=> x^{2}-8x+2x-16 = 0

=> x(x-8)+2(x-8) = 0

=> (x+2)(x-8) = 0

=> x = 8km/hr

Hence option [D] is correct answer.