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

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