A man swims downstream 51 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?
Select: A) 2 B) 8.5 C) 9.5 D) 6.5 E) 11.5
51 --- 3 DS = 17   ? ---- 1   18 ---- 3 US = 6   ? ---- 1 M = ?   M = (17 + 6)/2= 
<gadget id="calculator">(17 + 6)/2</gadget>
<output>23/2 = around 11.5</output>
11.5   Answer: 11.5
<result>E</result>
A man swims downstream 51 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?