Susan drove at an average speed of 30 miles per hour for the first 30 miles of a trip and then at an average speed of 60 miles per hour for the remaining 30 miles of the trip. If she made no stops during the trip, what was Susan's average speed, in miles per hour, for the entire trip?
+36915 Rate x time = distance
distance / rate = time
30 miles/ 30 m/hr = 1 hr
30 miles / 60 m/hr = 1/2 hr
(30 m + 30m) / (1 + 1/2 hr) = 60 m/1.5 hr = 40 m/hr average
