# A car travels up a hill at a constant speed of 35 km/h and returns down the hill at a constant speed of 66 km/h. How to calculate the average speed for the round trip ?

##### 1 Answer

Average speed

#### Explanation:

Define

Distance going up hill

Distance going down hill

Since the distances are equal

Suppose that it was a really long hill that took

In this case it would take

The total time taken would be

and

the total distance covered would be

and

the average speed would be

Notice that the proportions remain the same no matter what amount of time you assume it would take to go up the hill.