Answer:
First lets start with the simple One -
Velocity - Velocity is speed with Direction or in another words Displacement by time taken. So if a vehicle starts at A and Ends back at point A then the displacement is 0 hence the velocity is 0.
Speed - Assuming the distance between A to B while going from A to B is x kms
Case 1 - The Car goes returns from B to A via the same exact route it went from A to B. So the Average Speed will be total distance travelled by total time taken so .
Total Distance = x + x = 2x
Total Time = x/60 hrs + x/90 hrs = 3X+2X/180 = 5X/180
Average Speed = 2X*180/5X = 360/5 = 72km/hr
Case 2 - The Card goes to A to B via route 1 and returns back via Route 2 so one of the distances is X and the return distance is Y.
so now Average Speed = ((X+Y)/(3X+2Y)) *180
So in Case 2 if you substitute X = Y then also you get 2/5 * 180 = 72 Km / hr.
