Why is this not as simply as dividing it ?

Question

A car travels up a hill at a constant speed of 50 km/h and returns down the hill at a constant speed of 66 km/h. Calculate the average speed for the round trip.

because the answer I get is 16 km/hr because they are going in opposite directions

Answer 1

no man the answer is x times 2 divided by x/50 plus x/66 its 56.896552km/h

Answer 2

average speed is equal to the distance traveled divided by the elapsed time. so avg. speed=distance traveled/elapsed time.  What you calculated was the average velocity.  Speed is a scalar quantity which means it has no direction.