A man rows his boat downstream at 6 km/h and upstream at 4 km/h. What is the speed of the stream?

Explanation

The downstream speed (DS) is 6 km/h and the upstream speed (US) is 4 km/h. The speed of the stream (S) is calculated as half the difference between downstream and upstream speeds: S = (6 - 4) / 2 = 1 km/h.