Alberto has to go to the city to do some shopping and then come back home. I wanted to make the trip at an average of 60Km / h but due to traffic, the average speed of the outbound trip has been 30Km / h.
What average speed should I do on the return trip to finish the entire trip at an average speed of 60Km / h?
It is impossible to get the desired average on the return trip since regardless of the distance to the city you would have to travel twice the distance of the one-way trip in the same amount of time you spent on the one-way trip only.
We can see it more clearly with an example. If we assume that the distance to the city is 30km and its average one-way speed is 30km / h, it will take an hour to arrive. Now, to get an average speed of 60Km / h you should make the full round trip in one hour, but since you already spent that full hour on the outward journey, it would not be possible to return without increasing your total travel time.