TOM traveled the entire 100 miles trip. If he did the first 50 miles of at a constant rate 20miles 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? Choices:
A) 28.36 mph	B) 26.55 mph	C) 28.57 mph	D) 25.56 mph	E) 28.45 mph

Rationale: "avg speed = total distance / total time = ( d 1 + d 2 ) / ( t 1 + t 2 ) = ( 50 + 50 ) / ( ( 50 / 20 ) + ( 50 / 50 ) ) = 60 * 2 / 3 = 28.57 mph c"
Answer: C