A rower whose speed is 6 km/hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 3 km/hr. What is the rower's average speed (in km/hr) for the total journey? Choose the correct answer:
A) 3.9 B) 4.2 C) 4.5 D) 4.8 E) 5.1
time upstream = d / 3   time downstream = d / 9   total time = d/3 + d/9 = 4d/9   average speed = 2d / (4d/9) = 4.5 km/hr   The answer is 4.5.2  / (4 /9)= 
<gadget id="calculator">2  / (4 /9)</gadget>
<output>9/2 = around 4.5</output>
4.5 km/hr   The answer is 4.5.
<result>C</result>
A rower whose speed is 6 km/hr in still water rows to a certain point upstream and back to the starting point in a river which flows at 3 km/hr. What is the rower's average speed (in km/hr) for the total journey?