In a 100-mile trip, the first 30 miles were completed at 60 mph. If the average speed for the whole trip was 40 mph, what was the average speed in the last 70 miles?	Choices:	A) 30 mph	B) 32 mph	C) 35 mph	D) 37 mph	E) 38 mph

Rationale: the time to complete the first 30 miles was ( 30 miles / 60 mph ) = ( 1 / 2 ) hours . the time to complete the whole trip was ( 100 miles / 40 mph ) = ( 5 / 2 ) hours . the time to complete the last 70 miles was ( 5 / 2 ) - ( 1 / 2 ) = ( 2 ) hours . the average speed in the last 70 miles was ( 70 miles / 2 hours ) = 35 mph . the answer is c .
Answer: C