Average velocity = total displacement / total time
Total displacement is 25 yards.
Displacement is defined to be the change in the position of an object. Here displacement is 25 yards as firstly he walks 40 yards and again comes back 40 yards so he comes to original starting point. Now he again walks 50 yards and comes back 25 yards, so he is 25 yards from his starting position, hence displacement is 25.
Total time = 10 minutes
Average velocity = [tex]\frac{25}{10}[/tex] = 2.5 yards per minute.