A car travels from a to …

Let us assume the distance between A to B is x km. So , the car travels a total distance of (x+x) = 2x km. Now, the car travels at a speed of 20 km/hr from A to B . So, time taken by the car to reach at the point B from point A is given by, Car travels 20 km in 60 minutes. Car travels x km in (60÷20)×x minutes = 3x minutes Now, in the time of returning the car returns at a speed of 30 km/hr. So, time taken by the car to reach A from B is given by, Car travels 30 km in 60 minutes. Car travels x km in (60÷30)×x minutes = 2x minutes. So , the car takes a total time of ( 3x+2x)=5x minutes. Now , the average speed of the car for the whole journey is given by, In 5x minutes the car covers a distance of 2x km. So, in 60 minutes the car covers a distance of (2x÷5x)×60 km = 24 km. So , the average speed of the car for the whole journey is 24km/hr.