A man rows 24 km downstream in 2 hours and 15 km upstream in 3 hours. What is his speed in still water?

Explanation

1. 01

   Downstream speed $= \frac{24}{2} = 12$ km/h; upstream speed $= \frac{15}{3} = 5$ km/h.

2. 02

   Still water: $\frac{12 + 5}{2} = 8.5$ km/h.