A person rows a boat 85 km downstream and then 45 km upstream, taking 2.5 hours for each journey. What is the speed of the current?

Explanation

Calculate the downstream speed as distance divided by time: 85 km / 2.5 hours = 34 km/h. The upstream speed is 45 km / 2.5 hours = 18 km/h. The speed of the stream is half the difference between downstream and upstream speeds: (34 - 18) / 2 = 8 km/h.