TOM traveled the entire 80 miles trip. If he did the first 30 miles of at a constant rate 30 miles per hour and the remaining trip of at a constant rate 50 miles per hour, what is the his average speed, in miles per hour?  Answers.
A) 55 mph	B) 50 mph	C) 40 mph	D) 60 mph	E) 70 mph

Rationale: "avg speed = total distance / total time = ( d 1 + d 2 ) / ( t 1 + t 2 ) = ( 30 + 50 ) / ( ( 30 / 30 ) + ( 50 / 50 ) ) = 80 / 2 = 40 mph c"
Answer: C