Tara while driving to school computes the average speed for her trip to be 20 km/h. On her return trip along the same route, there is less traffic and the average speed is 40 km/h. What is the average speed for Tara's trip?
Let s be the distance between Tara's home and school.
Let t1 be the time in hours taken for going to school and t2 for returning back home.
So, t1 = sv1 = s20 h
and t2 = sv2 = s40 h
Total time taken, T = t1 + t2 = s20 h + s40 h = 3s40
Total distance = s + s = 2s
Hence, average speed = Total DistanceTotal Time = 2s(3s40) = 26.7 km/h