In one hour, a boat goes 6 km along the stream and 2 km against the stream. the sped of the boat in still water (in km/hr) is : Pick one:  A) 4  B) 5  C) 8  D) 9  E) 10

Rationale: "solution speed in still water = 1 / 2 ( 6 + 2 ) km / hr = 4 kmph . answer a"
Answer: A