A car travels from city A to city B at an average speed of 60 km/h and returns at an average speed of 40 km/h. What is the average speed for the round trip?
Correct: B
To find the average speed for a round trip, we use the formula: Average Speed = Total Distance / Total Time. Let's denote the distance from A to B as D. The time taken to travel from A to B is D / 60, and the time taken to travel back from B to A is D / 40. The total time is D / 60 + D / 40. Finding a common denominator, we get (2D + 3D) / 120 = 5D / 120 = D / 24. The total distance is 2D. Thus, the average speed = 2D / (D / 24) = 48 km/h.