Question

A motor boat heads upstream a distance of 24km in a river whose current is running at 3km/h . The trip up and back takes 6 hours. Assuming that the motor boat maintained a constant speed, what was its speed in still water

Answer 1

Step-by-step explanation:

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

Speed of boat in upstream = x - 3 km/hr

and in downstream = x + 3 km/ hr.

So 24/(x+3) + 24/(x-3) = 6

=> {24(x-3) + 24(x+3)}/(x+3)(x-3) = 6

=> 48x = 6(x^2 - 9)

=> 8z = x^2 - 9 => x^2 -8x -9 = 0

= (x-9)(x+1) = 0 => x = 9 or x = -1

x cannot be negative . So x = 9

Speed of boat = 9km/hr