SOLUTION: A car travels from A to B at a speed of 40mph and returns from B to A at 60mph. What is the average for the round trip? It says that the answer is 48mph, but I don't understand

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Question 551362: A car travels from A to B at a speed of 40mph and returns from B to A at 60mph. What is the average for the round trip?
It says that the answer is 48mph, but I don't understand why. It seems logical for the answer to be 50mph. However, I'm obviously missing something. Could you please explain in a simple and understandable way?
Answer by fcabanski(1391)   (Show Source): You can put this solution on YOUR website!
The average speed for the whole trip is the total distance traveled divided by the total time it took to travel that distance.


Distance = Rate * Time


The distance in both cases is the same, the rates are different and the times are different.


Call the time for A to B t and the time for B to A T
For A to B distance = 40t and for B to A the distance = 60T
The average speed for the trip is then (40t+60T)/(T+t)


Since the distances are the same we know 40t=60T and thus t = 60/40 * T = (3/2)T.


So the average speed is (40*(3/2)T + 60T)/(T+(3/2)T = 120T/(5/2)T = 120*2/5 = 48 MPH

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