A boy rides his bicycle 10 km at an average speed of 12 km/hr and again travels 12 km at an average speed of 10 km/hr. His average speed for the entire trip is approximately?
Options
A) 10.7 km / hr  B) 10.8 km / hr  C) 17.8 km / hr  D) 10.5 km / hr  E) 30.8 km / hr

Rationale: total distance traveled = 10 + 12 = 22 km / hr . total time taken = 10 / 12 + 12 / 10 = 61 / 30 hrs . average speed = 22 * 30 / 61 = 10.8 km / hr . answer : b
Answer: B