A man travels 160 km at 64 km/h and next 160 km at 80 km/h. What is the average speed over the first 320 km?

Average speed over multiple legs is total distance divided by total time, not the simple average of speeds.

Step-by-step calculation
Total distance = 160 + 160 = 320 kmTime₁ = 160 / 64 = 2.5 hTime₂ = 160 / 80 = 2 hTotal time = 2.5 + 2 = 4.5 hAverage speed = 320 / 4.5 = 71.11 km/h (approx.)

Verification / Alternative
For two equal distances d at speeds v₁, v₂: Harmonic mean applies: Average speed = (2d) / (d/v₁ + d/v₂) which is the same calculation above.

Common pitfalls
Do not average 64 and 80 directly; that would ignore time spent at each speed.

Final Answer
71.11 km/h