Susan drove an average speed of 30 mph for the first 30 miles of a trip. She did drove 60 mph for the next 30 miles. If she made no stops, what was the average speed, in miles per hour, for the entire trip?
a. 35 b. 40 c. 45 d. 50 e. 55

Avg Speed = Total Dist/ Total Time. = 30 + 30 / 1 + 1/2 = 40