A truck driver drove 320 miles in 4 hours, then 360 miles in 6 hours. What was the average speed over the entire trip?

Average speed over entire trip = total distance / total time. Total distance: 320 + 360 = 680 miles. Total time: 4 + 6 = 10 hours. Average speed: 680/10 = 68 mph. Important: this is NOT the average of the two individual speeds! Speed 1: 320/4 = 80 mph; Speed 2: 360/6 = 60 mph. Simple average of speeds: (80 + 60)/2 = 70 mph — this is WRONG because the driver spent different amounts of time at each speed. Average speed must be calculated from total distance divided by total time, weighting each speed by its duration. This is a common ASVAB trick question. The principle applies to any 'weighted average' problem: a class average where different sections have different student counts, an investor's return over different periods with different amounts invested, etc. Always think: what does 'average' actually mean for this quantity? Distance ÷ time is the actual definition of average speed; it cannot be averaged any other way.