A boat goes 20 km downstream in one hour and the same distance upstream in two hours The speed of th...........

Explanation:

Downstream speed, D = 20 km/ 1 hr. – 20 km/hr
Upstream speed, U = 20 km/ 2hr. = 10 km/hr
Speed of the boat in still water , x
= (D + U)/2
= (20 + 10)/2 = 30/2 = 15 km/hr.