A car travels first 160 km at 90 km/hr and the next 160 km at 80 km/hr. What is the average speed for the first 320 km of the tour?  Options:  A) 71.11  B) 84.7  C) 71.1  D) 71.17  E) 71.13

Rationale: "car travels first 160 km at 90 km / hr time taken to travel first 160 km = distancespeed = 160 / 90 car travels next 160 km at 80 km / hr time taken to travel next 160 km = distancespeed = 160 / 80 total distance traveled = 160 + 160 = 2 × 160 total time taken = 160 / 90 + 160 / 80 average speed = total distance traveled / total time taken = 320 / ( 160 / 90 + 160 / 80 ) = 84.7 km / hr answer : b"
Answer: B