Answer:45 mi/h
Step-by-step explanation:
Recall: Speed = distance / time
Let the time taken for the morning journey be and the time taken for the afternoon journey be ,and the distance covered be d
that means for the first journey,
30 =
d = 30
Also for the afternoon journey,
d = 60
Equating the two , since the same distance is being covered , we have
30 = 60
that is
=
= 2
Also ,
total distance covered = 30 + 60
Average speed = total distance / total time
= 30 + 60 / +
Recall that = 2 , substitute this into the formula for average speed , then we have
Average speed = 30(2) +60 / 3
Average speed = 120 / 3
Therefore :
Average speed = 40 mi/hr