Jack and Jill are marathon runners. Jack can finish a marathon (40 km) in 4.5 hours and Jill can run a marathon in 4.0 hours.What is the ratio of their average running speed? (Jack: Jill)	Answers.
A) 14 / 15	B) 15 / 14	C) 8 / 9	D) 5 / 4	E) can not be determined

Rationale: "average speed of jack = distance / time = 40 / ( 9 / 2 ) = 80 / 9 average speed of jill = 40 / ( 4.0 ) = 10 ratio of average speed of jack to jill = ( 80 / 9 ) / 10 = 8 / 9 answer c"
Answer: C