A car travels the first 160 km at a speed of 64 km/h and the next 160 km at a speed of 80 km/hr What is the average speed for the first 320 km of the tour?

Distance for the first part of the trip = 160 km, speed = 64 km/h.

Distance for the second part of the trip = 160 km, speed = 80 km/h.

​$$\text{Average Speed} = \frac{2 \times \text{Speed}_1 \times \text{Speed}_2}{\text{Speed}_1 + \text{Speed}_2}.$$​​

Using the formula for average speed:

​$$\text{Speed}_1 = 64 \, \text{km/h} \\\text{Speed}_2 = 80 \, \text{km/h} \\\text{Average Speed} = \frac{2 \times 64 \times 80}{64 + 80} = \frac{2 \times 5120}{144} = \frac{10240}{144} \approx 71.11 \, \text{km/h}.$$