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, we need to find the total distance traveled and the total time taken. Since the distance from A to B is the same as from B to A, let's denote this distance as d. The time taken to travel from A to B is d/60 and the time taken to travel from B to A is d/40. The total time is d/60 + d/40. To add these fractions, we find a common denominator: (2d + 3d)/120 = 5d/120. The total distance is 2d. The average speed is total distance / total time = 2d / (5d/120) = 2d * 120 / 5d = 240 / 5 = 48 km/h.