A cyclist rides a bicycle 9 km at an average speed of 12 km/hr and again travels 12 km at an average speed of 9 km/hr. What is the average speed for the entire trip?  Answers:	A) 9.5	B) 9.8	C) 10.1	D) 10.6	E) 11.2

Rationale: "distance = 21 km time = 9 / 12 + 12 / 9 = ( 81 + 144 ) / 108 = 225 / 108 = 25 / 12 hours average speed = ( 21 * 12 ) / 25 = 10.1 km / h the answer is c ."
Answer: C