A man rows 0.75 kilometers upstream in 11 minutes and 15 seconds, and returns downstream covering the same distance in 7 minutes and 30 seconds. What is his speed in still water?

Explanation

The man rows 0.75 km upstream in 11.25 minutes and the same distance downstream in 7.5 minutes. Converting times to hours: upstream time = 11.25/60 = 0.1875 hr, downstream time = 7.5/60 = 0.125 hr. Upstream speed = 0.75 / 0.1875 = 4 km/hr, downstream speed = 0.75 / 0.125 = 6 km/hr. The speed in still water is the average of upstream and downstream speeds: (4 + 6) / 2 = 5 km/hr.