OK, i see. from the beginning then:
A»B, we say is distance "D"
1)a»b, 5m/s
2)b»a, 3 m/s
V=Distance/time
time=D/V «» time(1)=d/5m/s time(2)=d/3m/s
Total time= d/5 + d/3= 5d+3d/15= 8d/15.
Total distance=d+d=2d
V(average)=total D/total T
=2d/(8d/15) = 30d/8d = 3,75.
That help? =)
