A car travels 120 miles in 2 hours, then travels an additional 180 miles in 3 hours. What is the car's average speed for the entire trip,…

Average speed is total distance divided by total time, not the average of the two speeds. The total distance is $120 + 180 = 300$ miles and the total time is $2 + 3 = 5$ hours, so the average speed is $\frac{300}{5} = 60$ miles per hour, choice D. The two segment speeds are 60 mph and 60 mph, so the average is consistent. Choice A (65) and choice C (75) are numbers that do not follow from the data and likely come from arithmetic slips such as adding speeds. Choice B (50) comes from dividing the total distance by 6 hours, an incorrect time total.