A car travels from city A to city B at an average speed of 40 mph and returns at an average speed of 60 mph. What is the average speed for the round trip?
Correct: B
The average speed for a round trip is calculated using the formula: Average Speed = Total Distance / Total Time. Let's denote the distance from A to B as D. The time to travel from A to B is D/40, and the time to return from B to A is D/60. The total time is D/40 + D/60. To add these fractions, we find a common denominator, which is 120. This gives us (3D + 2D)/120 = 5D/120 = D/24. The total distance for the round trip is 2D. Therefore, the average speed = Total Distance / Total Time = 2D / (D/24) = 48 mph.