1. **State the problem:** Lee cycles 60 km at 30 km/h and returns 60 km at 20 km/h. We need to find the average speed for the entire journey. 2. **Formula for average speed:** Average speed for a round trip when speeds differ is given by the harmonic mean formula: $$\text{Average speed} = \frac{2 \times v_1 \times v_2}{v_1 + v_2}$$ where $v_1$ and $v_2$ are the speeds for the two parts of the trip. 3. **Calculate using given speeds:** $$v_1 = 30, \quad v_2 = 20$$ 4. **Apply the formula:** $$\text{Average speed} = \frac{2 \times 30 \times 20}{30 + 20} = \frac{1200}{50} = 24$$ 5. **Interpretation:** The average speed for the whole journey is 24 km/h. This method works because the distances are equal, so the harmonic mean gives the correct average speed over the entire trip.