Question

A car travels up a hill at a constant speed of 34 km/h and returns down the hill at a constant speed of 66 km/h. Calculate the average speed for the round trip.

Answer 1

Here

Define
t1= time spent going up hill
t2= time spent going down hill

Distance going up hill =34 kmhr⋅t1 hr

Distance going down hill =66 kmhr⋅t2 hr

Since the distances are equal
34t1=66t2

Suppose that it was a really long hill that took 66 hr to go up.
In this case it would take 34 hr to go down.
The total time taken would be 66+34=100 hr
and
the total distance covered would be 34 kmhr⋅66 hr+34 kmhr⋅34 hr=3400 km
and
the average speed would be 3400 km100 hr=34 km/hr