A cyclist rides 6 km uphill at 9 km/h, then 6 km downhill at 18 km/h, and finally 12 km on a level road at 12 km/h. What is his average speed for the ride?

Explanation

1. 01

   Uphill time $= \frac{6}{9} = \frac{2}{3}$ h; downhill $= \frac{6}{18} = \frac{1}{3}$ h; level $= \frac{12}{12} = 1$ h.

2. 02

   Total time = 2 h; total distance = 24 km.

3. 03

   Average speed $= \frac{24}{2} = 12$ km/h.