A man rows a boat at 5 km/h in still water. If his speed against the current is 3.5 km/h, what is his speed when rowing with the current?

Explanation

The speed in still water is the average of the speeds against and along the current. Given the speed against the current is 3.5 km/h and the still water speed is 5 km/h, the speed with the current is calculated as 2 × 5 - 3.5 = 6.5 km/h.