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 entire trip?
Correct: A
To find the average speed for the entire trip, we can use the formula: average speed = total distance / total time. Since the distance from A to B is the same as from B to A, we can let the distance be d. The time it takes to travel from A to B is d/60 and the time it takes to travel from B to A is d/40. So, the total time is d/60 + d/40. The total distance is 2d. Therefore, the average speed is 2d / (d/60 + d/40) = 2 / (1/60 + 1/40) = 2 / (4/240 + 6/240) = 2 / (10/240) = 2 * 240 / 10 = 48 km/h.