A cyclist rides a bicycle 8 km at an average speed of 10 km/hr and again travels 10 km at an average speed of 8 km/hr. What is the average speed for the entire trip?	Choose the most appropriate option.
A) 9.28  B) 8.48  C) 8.78  D) 8.98  E) 9.18
distance = 18 km   time = 8/10 + 10/8 = (64 + 100) / 80 = 164 / 80 = 41 / 20 hours   average speed = (18 * 20) / 41 = 8.78 km/h   The answer is 8.78.
<result>C</result>
A cyclist rides a bicycle 8 km at an average speed of 10 km/hr and again travels 10 km at an average speed of 8 km/hr. What is the average speed for the entire trip?