A rower whose speed is 8 km/hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 4 km/hr. What is the rower's average speed (in km/hr) for the total journey?  Choose the correct option
A) 5  B) 6  C) 7  D) 8  E) 9
time upstream = d / 4   time downstream = d / 12   total time = d/4 + d/12 = d/3   average speed = 2d / (d/3) = 6 km/hr   The answer is 6.
<result>B</result>
A rower whose speed is 8 km/hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 4 km/hr. What is the rower's average speed (in km/hr) for the total journey?