In one hour,a boat goes 8 km along the stream and 2 km against the stream.The speed of the boat in still water (in km/hr) is : Select the correct option
A) 3  B) 5  C) 8  D) 9  E) 10

Rationale: "solution speed in still water = 1 / 2 ( 8 + 2 ) kmph . = 5 kmph . answer b"
Answer: B