Question

a boat travels 30 km up a river in the same time it takes to travel 50 km down the same river. if the current water is 5 km per hour , what is the speed of the boat in still water?

Answer 1

Solution :  Let speed of boat in still water = x km/h  Speed of the boat downstream = x + 5  Speed of the boat upstream = x - 5  Speed = Distance / time  So time = Distance / speed Time taken by boat to travel 30 km upstream = 30/ (x – 5)  Time taken by boat to travel 50 km downstream = 50/ (x + 5)  Since time taken by the boat in both cases is the same ,    => 30 (x + 5) = 50 (x -5) => 30 x +150 = 50x -250 => 20x = 400 => x = 20 Thus the speed of the boat in still water is 20 km/h.