A man can row a boat at a speed of 20 km/hr in still water. If the speed of the stream is 5 km/hr, in what time in hours he can row a distance of 75 km downstream?

3

Let the speed of boat be x km/hr and the speed of stream be y km/hr. 

Downstream_speed = x + y km/hr i.e. 20 + 5 = 25km/hr

Downstream_speed = \(\frac{\text{Downstream distance}}{\text{Downstream time}}\)

Downstream_time = \(\frac{\text{Downstream distance}}{\text{Downstream speed}}\)

Downstream_{time =}  \(\frac{75 }{ 25}\) 

Downstream_time = 3