To calculate the average velocity, we need to consider both the distance traveled and the time taken. Average velocity is defined as the total displacement divided by the total time.
In this case, the car travels 55 km south and then 25 km north, resulting in a net displacement of 55 km - 25 km = 30 km to the south.
The total time taken is 1.5 hours.
To calculate the average velocity, we divide the net displacement by the total time:
Average velocity = Net displacement / Total time
Average velocity = 30 km / 1.5 hr
Average velocity = 20 km/hr
Therefore, the average velocity of the car is 20 km/hr to the south.